I have been using the following command to open another MDB Access file via VBA:
Shell \"cmd /c \" & Chr(34) & strNewFullPath & Chr(34), vbHide
You can use the Win32 API to find the EXE name associated with the file type and prepend it to your shell command like this:
Private Declare Function FindExecutable Lib "shell32.dll" Alias "FindExecutableA" (ByVal lpFile As String, ByVal lpDirectory As String, ByVal lpResult As String) As Long
Public Function GetExecutableForFile(strFileName As String) As String
Dim lngRetval As Long
Dim strExecName As String * 255
lngRetval = FindExecutable(strFileName, vbNullString, strExecName)
GetExecutableForFile = Left$(strExecName, InStr(strExecName, Chr$(0)) - 1)
End Function
Sub RunIt(strNewFullPath As String)
Dim exeName As String
exeName = GetExecutableForFile(strNewFullPath)
Shell exeName & " " & Chr(34) & strNewFullPath & Chr(34), vbNormalFocus
End Sub