Just a few notes:
1. Make sure if you added the user you are testing the INGROUP with, that that user has logged of and logged on again so his token is updated.
2. run kix32 -f (Flush tokencache) to make sure there are no errors there.

I'm also on Windows 7 and with a 2000 AD and I have no problems so far. But I'll check monday and test a few things.