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!!!