I
googled[
^] and found
this[
^].
They use similar code to yours to find if it's Vista:
Public Function IsVista() As Boolean
If Environment.OSVersion.Version.Major = 6 Then
Return True
Else
Return False
End If
End Function
I'm assuming that the major version would be 7 for windows 7. At least this might help get you started or be another train of thought to research.
EDIT - Guess you need to check minor version too, and Win 7 is 6.1.