I have just installed Vista Ultimate 64 (Legit).
Installed latest drivers for everything and it runs really well.
Only problem is the media player visualizations are really low res and very choppy in full screen mode.
The Gfx card has been rated at 5.9 and Aero/Games work fine with no lag.. Also watching 1080p movies as well with no issues. Dxdiag reports no errors and acceleration is on full