Hola podes usar la Api GetVersion de esta forma
Private Declare Function GetVersion Lib "kernel32" () As Long
Public Function GetWinVersion() As String
Dim Ver As Long, WinVer As Long
Ver = GetVersion()
WinVer = Ver And &HFFFF&
'retrieve the windows version
GetWinVersion = Format((WinVer Mod 256) + ((WinVer \ 256) / 100), "Fixed")
End Function
Private Sub Form_Load()
MsgBox "Windows version: " + GetWinVersion
End Sub
Este ejemplo lo saque del URL:
http://www.allapi.net/
fijate en este link
http://www.mentalis.org/apilist/GetVersion.shtml que te explica bien las cosas
Bye!!!