Simple really, and I guess the answer depends on if anyone has Vista-only games or has heard elsewhere. The likes of Halo 2 and Shadowrun are marked as Vista-only and don't work under previous OS's such as XP etc. I've got the Win 7 Beta burned, and am just backing up some of data now, but just thought about this potential problem this very moment. If Halo 2 PC does not work under the Windows 7 Beta, then I won't be installing Windows 7 tonight. Hopefully someone can have an answer for me as I was hoping to try out Windows 7 later tonight.