I can only tell you I my personal experience with x64 Windows. I got the new 4000+ and tried to install it (three times). For some reason, there was serious driver issues when loading up the Asus provided drivers (the x64 variant) with the new OS. I think I had narrowed it down to the IDE drivers that Asus/Nforce wanted to install, but by that time I said the heck with this and went with stock XP-SP1.