Pareceser que hay que añadir unas claves al registro... 
puede hacerse generando un fichero .reg 
con las claves preparadas y usando el regedit en modo silencioso

el comando es:
  regedit /s fichero.reg


la claves son:
HKCR\{ext}  = {typeAbr}
HKCR\{typeAbr}\ = {typeName}
HKCR\{typeAbr}\DefaultIcon = {FileIcon}
HKCR\{typeAbr}\shell\open\command = {exeCommand}


estas no parecen necesarias:
HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\{ext}\Application = {exeName}
HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\{ext}\OpenWithList\a = {exeName}

donde:
{ext} = ".gvp"
{typeAbr} ="gvSIGProject"
{typeName} ="gvSIG Project file"
{FileIcon} = "gvSIG.ico" || "gvSIG.exe"
{exeCommand} = "gvSIG.exe %L"
{exeName} = "gvSIG.exe"


Ejeplo de fichero .reg:
REGEDIT4

[HKEY_CLASSES_ROOT\.gvp]
@="gvSIGProject"

[HKEY_CLASSES_ROOT\gvSIGProject]
@="gvSIG Project file"

[HKEY_CLASSES_ROOT\gvSIGProject\DefaultIcon]
@="C:\\Archivos de programas\\gvSIG_1.0\\bin\\ico-gvSIG.ico,0"


[HKEY_CLASSES_ROOT\gvSIGProject\shell\open]
@="Abrir"

[HKEY_CLASSES_ROOT\gvSIGProject\shell\open\command]
@="C:\\Archivos de programas\\gvSIG_1.0\\bin\\gvSIG.exe \"%1\""













*******************************************************************
URL's y recortes:


http://en.wikipedia.org/wiki/Windows_registry

http://www.akadia.com/services/windows_registry_tutorial.html

http://webtools.live2support.com/windows/







http://www.freevbcode.com/ShowCode.asp?ID=2799
******************
usando VB


Public Sub associate(EXT As String, FileType As String, _
   FileName As String)
On Error Resume Next
Dim b As Object
Set b = CreateObject("wscript.shell")
b.regwrite "HKCR\" & EXT & "\", FileType
b.regwrite "HKCR\" & FileType & "\", "MY file"
b.regwrite "HKCR\" & FileType & "\DefaultIcon\", FileName
b.regwrite "HKCR\" & FileType & "\shell\open\command\", _
   FileName & " %L"
b.regdelete "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\" & EXT & "\Application"
b.regwrite "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\" & EXT & "\Application", FileName
b.regdelete "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\" & EXT & "\OpenWithList\"
b.regwrite "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\" & EXT & "\OpenWithList\a", FileName

End Sub

'Sample Usage
Private Sub Form_Load()
associate ".jpg", "JPGFile", _
   "C:\Program Files\Accessories\MSPAINT.EXE"
Unload Me
End Sub


****************


http://www.ss64.com/nt/:
http://www.ss64.com/nt/ftype.html
**************************************************************************
FTYPE

Display or change the link between a FileType and an executable program

Syntax
   FTYPE fileType=executable_path

   FTYPE

   FTYPE fileType

   FTYPE fileType=

Key
   fileType        : The type of file

   executable_path : The executable program including any command line parameters             

More than one file extension may be associated with the same File Type.
e.g. both the extension .JPG and the extension .JPEG may be associated with the File Type "jpegfile"

File Types can be displayed in the Windows Explorer GUI: [View, Options, File Types] however the spelling is usually different to that expected by the FTYPE command e.g. the File Type "txtfile" is displayed in the GUI as "Text Document"and "jpegfile" is displayed as "image/jpeg"

Several FileTypes can be linked to the same executable application, but
one FileType cannot be linked to more than one executable application.

FTYPE file type will display the current executable program for that file type.

FTYPE without any parameters will display all FileTypes and the executable program for each.

Defining command line parameters

It is almost always necessary to supply command line parameters so that when a document is opened not only is the relevant application loaded into memory but the document itself also loaded into the application. To make this happen the filename of the document must be passed back to the application.

Command line parameters are exactly like batch file parameters, %0 is the executable program and %1 will reference the document filename

so a simple command line might be:

MyApplication.exe "%1"

If any further parameters are required by the application they can be passed as %2, %3. To pass ALL parameters to an application use %*. To pass all the remaining parameters starting with the nth parameter, use %~n where n is between 2 and 9.

The FileType should always be created before making a File Association

For example:

FTYPE htmlfile="C:\PROGRA~1\Plus!\MICROS~1\iexplore.exe" -nohome
ASSOC .html=htmlfile

FTYPE pagemill.html=C:\PROGRA~1\Adobe\PAGEMI~1.0\PageMill.exe "%1"
ASSOC .html=pagemill.html

FTYPE rtffile="C:\Program Files\Windows NT\Accessories\WORDPAD.EXE" "%1"
ASSOC .rtf=rtffile

FTYPE word.rtf.8="C:\Program Files\Microsoft Office\Office\winword.exe" /n
ASSOC .rtf=word.rtf.8

Switching a File Association between multiple applications

If you have multiple applications that use the same file extension, the ASSOC command can be used to switch the file extension between the different FileTypes.

Deleting a FileType

Specify executable_path=nothing and the FTYPE command will delete the executable_path for that FileType.
For example:
FTYPE htmlfile=

Backing up your FileTypes

FTYPE >backup_types.txt
ASSOC >backup_ext.txt

Restoring your FileTypes from a Backup

FOR /F "tokens=* delims=" %G IN (backup_types.txt) DO FTYPE %G
FOR /F "tokens=* delims=" %G IN (backup_ext.txt) DO ASSOC %G

This will recreate the CLASS id's in the registry at HKey_Classes_Root\.<file extension>
If you put the commands above in a batch file change the %G to be %%G

Using File associations at the command line

If you have a file association between .DOC and Word for Windows then at a command prompt you can open a document with any of the following commands:

Start "My Document.doc"
"Monthly Report.doc"
JULY.DOC

note that the file extension must be supplied for this to work

"True to type - Of a plant, or group of plants, which matches the accepted description of the cultivar to which it is assumed to belong"

Related Commands:

ASSOC - Change file extension associations
Batch file to list the application associated with a file extension
ASSOCIAT - One step file association (Resource Kit)

**************************************************************************

http://www.ss64.com/nt/assoc.html
*************************************************************************

ASSOC

Display or change the association between a file extension and a fileType

Syntax
   ASSOC .ext = [fileType]
   ASSOC
   ASSOC .ext
   ASSOC .ext =

Key
    .ext      : The file extension
    fileType  : The type of file 

A file extension is the last few characters in a FileName after the period.
So a file called JANUARY.HTML has the file extension .HTML

The File extension is used by Windows NT to determine the type of information stored in the file and therefore which application(s) will be able to display the information in the file. File extensions are not case sensitive and are not limited to 3 characters.

More than one file extension may be associated with the same File Type.
e.g. both the extension .JPG and the extension .JPEG may be associated with the File Type "jpegfile"

At any one time a given file extension may only be associated with one File Type.
e.g. If you change the extension .JPG so it is associated with the File Type "txtfile" then it's normal association with "jpegfile" will disappear. Removing the association to "txtfile" does not restore the association to "jpegfile"

File Types can be displayed in the Windows Explorer GUI: [View, Options, File Types] however the spelling is usually different to that expected by the ASSOC command e.g. the File Type "txtfile" is displayed in the GUI as "Text Document"and "jpegfile" is displayed as "image/jpeg"

The command ASSOC followed by just a file extension will display the current File Type for that extension.

ASSOC without any parameters will display all the current file associations.

ASSOC with ".ext=" will delete the association for that file extension.

Did you leave the Always Use This Program To Open This File option turned on?
To change it back so it prompts you to specify a program each time, just delete the association for that file type
ASSOC .ext=
[where .ext is the file extension].
Now when you double-click on a file of that type, the system will ask you what program you want to use.

Using the ASSOC command will edit values stored in the registry at HKey_Classes_Root\.<file extension>
Therefore it's possible to use registry permissions to protect a file extension and prevent any file association changes.

Examples:

Viewing file associations:

ASSOC .txt
ASSOC .doc
ASSOC >backup.txt

Editing file associations:

ASSOC .txt=txtfile
ASSOC .DIC=txtfile
ASSOC .html=Htmlfile

Deleting a file association:

ASSOC .html=

Repair .REG and .EXE file associations:

ASSOC .EXE=exefile
ASSOC .REG=regfile

Digging through CLASSES_ROOT entries often reveals more than one shell for the same application, for example the Apple Quick Time player has two entries, one to "open" (which gives an annoying nag screen) and one to just "play" the QT file:
[HKEY_CLASSES_ROOT\MOVFile\shell\open] and [play]

In cases like this you can change the default action e.g.
[HKEY_CLASSES_ROOT\MOVFile\shell]
@="play"

"Of all forms of caution, caution in love is perhaps the most fatal to true happiness" - Bertrand Russell

Related:

FTYPE - Edit file types (used in file extension associations)
Batch file to list the application associated with a file extension
ASSOCIAT - One step file association (Resource Kit)
Q162059 - Associate Internet Explorer with MS Office files
JSIFAQ - Tip 9715 - List File Types with executable path

****************************************************************


http://www.ss64.com/nt/associate.html
**********************************************************************
ASSOCIATE.exe (Resource Kit)

One step file association.

This utility does the job of both ASSOC and FTYPE, in one step. ASSOCIATE assigns an extension directly with an executable application. This is done by automatically adding a new FileType to the system registry.

Syntax
      ASSOCIATE .ext filename [/q /d /f]

Key
   .ext     : Extension to be associated.
   filename : Executable program to associate .ext with.
   /q       : Quiet - Suppress interactive prompts.
   /f       : Force - Force overwrite or delete without questions.
   /d       : Delete - Delete the association.

A file extension is the last few characters in a FileName after the period.
So a file called JANUARY.HTML has the file extension .HTML

The File extension is used by Windows NT to determine the type of information stored in the file and therefore which application(s) will be able to display the information in the file. File extensions are not case sensitive and are not limited to 3 characters.

Example: adding a File Association

To add the File Type "SQLfile"=Notepad.exe and also set the File Association of .SQL="SQLfile" run this command:

ASSOCIATE .SQL Notepad.exe

Example: Removing a File Association

ASSOCIATE .SQL /d

Note that /d will delete the File Association but will NOT delete the File Type.

File types created by Associate.exe are always given a name in the form xxxfile, where xxx is the file extension.

"There are three roads to ruin; women, gambling and technicians. The most pleasant is with women, the quickest is with gambling, but the surest is with technicians" - Georges Pompidou

Related Commands:

ASSOC Change file extension associations
FTYPE Display or modify file types used in file extension associations
**********************************************************************




WINDOWS 98


http://groups.google.com/group/alt.msdos.batch/browse_thread/thread/556321da29c9ca2e/e60e3330cd284b99?lnk=gst&q=file+association&rnum=2#e60e3330cd284b99
***************************************************************************

	
De:		William Allen - ver perfil
Fecha:		Mié 26 mar 2003 14:28
Correo electrónico: 		"William Allen" <_inval...@mayfly13.fsnet.co.uk>
Grupos: 		alt.msdos.batch
Sin calificar
Valoración:	 
mostrar opciones
Responder | Responder al autor | Reenviar | Imprimir | Mensaje individual | Mostrar mensaje original | Notificar abuso | Buscar mensajes de este autor

"Robert Mark Bram" wrote in message
> I recently asked this question in alt.msdos.batch.nt -- but I need an answer
> for Win 98..

> Can use a batch file to create a windows file association?

Yes. Windows 95/98/ME users can use the Windows 98 Resource Kit
utility ASSOCIAT.EXE (cloned from the NT4 Resource Kit), which will
operate with the Windows 95/98/ME registries to create file associations
very easily. ASSOCIAT.EXE provides an informative ERRORLEVEL and
is designed for use in Batch files. Downloadable free from the Microsoft FTP site:
ftp://ftp.microsoft.com/Services/TechNet/samples/ps/win98/Reskit/FILE/

and click on file: ASSOCIAT.EXE

For syntax help with using ASSOCIAT.EXE, use the /? switch
associat /?

Full documentation, usage instructions, and syntax examples for Batch
usage of all the Windows 98 Resource Kit Batch tools (which you can
use in Windows 95 and ME, too):
ftp://ftp.microsoft.com/Services/TechNet/samples/ps/win98/reskit/help...
This is a fully indexed and searchable compiled help file. Although
each utility responds to the usual /? for brief help, this main file has
huge detail. When you have the file, look in the Contents section
under "Scripting Tools". 


*************************************************************************

PARA TODOS LOS WINDOWS

http://www.robvanderwoude.com/index.html
http://www.robvanderwoude.com/files/defopen.txt

defopen.bat

Create a default file association to Notepad and add "Open with Notepad", "Print with Notepad" and "Command Prompt Here" options to popup menus

************************************************************************
@ECHO OFF
:: No parameters required
IF NOT [%1]==[] GOTO Syntax

:: Choose the correct command processor for the current operating system
SET _cmd=
:: Variable to add shortcut to menu entry (NT only,
:: since COMMAND.COM cannot echo an ampersand)
SET _=
ECHO.%COMSPEC% | FIND /I "command.com" >NUL
IF NOT ERRORLEVEL 1 SET _cmd=command.com /e:4096
ECHO.%COMSPEC% | FIND /I "cmd.exe" >NUL
IF NOT ERRORLEVEL 1 SET _cmd=cmd.exe
IF [%_cmd%]==[cmd.exe] SET _=^&

:: Create a temporary .REG file
> "%Temp%.\DefOpen.reg" ECHO REGEDIT4
>>"%Temp%.\DefOpen.reg" ECHO.
ECHO Adding "Open with Notepad" entry
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\*\shell\open]
>>"%Temp%.\DefOpen.reg" ECHO @="%_%Open with Notepad"
>>"%Temp%.\DefOpen.reg" ECHO.
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\*\shell\open\command]
>>"%Temp%.\DefOpen.reg" ECHO @="notepad.exe \"%%1\""
>>"%Temp%.\DefOpen.reg" ECHO.
ECHO Adding "Print with Notepad" entry
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\*\shell\print]
>>"%Temp%.\DefOpen.reg" ECHO @="%_%Print with Notepad"
>>"%Temp%.\DefOpen.reg" ECHO.
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\*\shell\print\command]
>>"%Temp%.\DefOpen.reg" ECHO @="notepad.exe /p \"%%1\""
>>"%Temp%.\DefOpen.reg" ECHO.

:: If neither COMMAND.COM nor CMD.EXE then skip this step
IF [%_cmd%]==[] ECHO Skipping "Command Prompt Here" entry
IF [%_cmd%]==[] GOTO Merge

ECHO Adding "Command Prompt Here" entry
:: Add Command Prompt Here for files
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\*\shell\prompt]
>>"%Temp%.\DefOpen.reg" ECHO @="Command Prompt Here"
>>"%Temp%.\DefOpen.reg" ECHO.
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\*\shell\prompt\command]
>>"%Temp%.\DefOpen.reg" ECHO @="%_cmd% /k cd \"%%1\\..\""
>>"%Temp%.\DefOpen.reg" ECHO.
:: Add Command Prompt Here for directories
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\Directory\shell\prompt]
>>"%Temp%.\DefOpen.reg" ECHO @="Command Prompt Here"
>>"%Temp%.\DefOpen.reg" ECHO.
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\Directory\shell\prompt\command]
>>"%Temp%.\DefOpen.reg" ECHO @="%_cmd% /k cd \"%%1\""
>>"%Temp%.\DefOpen.reg" ECHO.
:: Add Command Prompt Here for drives
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\Drive\shell\prompt]
>>"%Temp%.\DefOpen.reg" ECHO @="Command Prompt Here"
>>"%Temp%.\DefOpen.reg" ECHO.
>>"%Temp%.\DefOpen.reg" ECHO [HKEY_CLASSES_ROOT\Drive\shell\prompt\command]
>>"%Temp%.\DefOpen.reg" ECHO @="%_cmd% /k cd \"%%1\""
>>"%Temp%.\DefOpen.reg" ECHO.

:: Merge the temporary .REG file
:Merge
START /WAIT REGEDIT /S "%Temp%.\DefOpen.reg"

:: Delete the temporary .REG file
DEL "%Temp%.\DefOpen.reg"

:: Ready
GOTO End

:Syntax
ECHO.
ECHO DefOpen.bat,  Version 3.00 for Windows 95/98/NT 4/2000/XP
ECHO Adds a default association: when a file without a file association
ECHO is double-clicked, it will be opened with Notepad.
ECHO Adds three new entries to the right mouse button menu as well:
ECHO "Open with Notepad", "Print with Notepad" and "Command Prompt Here".
ECHO.
ECHO Usage:  DEFOPEN
ECHO.
ECHO Written by Rob van der Woude
ECHO http://www.robvanderwoude.com
ECHO Notepad registry tip courtesy of Regedit.com
ECHO http://www.regedit.com

:: Clean up variables and quit
:End
SET _cmd=
SET _=
*****************************