Binaryworld - CreateFileAssociation - Associate a file extension to a program ... [ VB -> Windows ]

Private Declare Sub SHChangeNotify Lib "shell32.dll" (ByVal wEventId As Long, _
  ByVal uFlags As Long, ByVal dwItem1 As Long, ByVal dwItem2 As Long)
Const SHCNE_ASSOCCHANGED = &H8000000
Const SHCNF_IDLIST = 0

' Create the new file association
'
' Extension is the extension to be registered (eg ".cad"
' ClassName is the name of the associated class (eg "CADDoc")
' Description is the textual description (eg "CAD Document"
' ExeProgram is the app that manages that extension (eg "c:\Cad\MyCad.exe")
'
' NOTE: requires CreateRegistryKey and SetRegistryValue functions

Sub CreateFileAssociation(ByVal Extension As String, ByVal ClassName As String, _
  ByVal Description As String, ByVal ExeProgram As String)
  Const HKEY_CLASSES_ROOT = &H80000000

  ' ensure that there is a leading dot
  If Left(Extension, 1) <> "." Then
    Extension = "." & Extension
  End If

  ' create a new registry key under HKEY_CLASSES_ROOT
  CreateRegistryKey HKEY_CLASSES_ROOT, Extension
  ' create a value for this key that contains the classname
  SetRegistryValue HKEY_CLASSES_ROOT, Extension, "", ClassName
  ' create a new key for the Class name
  CreateRegistryKey HKEY_CLASSES_ROOT, ClassName & "\Shell\Open\Command"
  ' set its value to the command line
  SetRegistryValue HKEY_CLASSES_ROOT, ClassName & "\Shell\Open\Command", "", _
    ExeProgram & " ""%1"""

  ' notify Windows that file associations have changed
  SHChangeNotify SHCNE_ASSOCCHANGED, SHCNF_IDLIST, 0, 0
End Sub