Well, there really isn't a reason to use Vista anymore. They finally released the working Alpha of DX10 for XP. Enjoy.
DX10 for XP Alpha
Hmm... When I want to play games, I want to play games and think about games and not about computers. The games I play work just fine on XP with dx9c and I have Vista on another partition just in case I will really need dx10 in the future.
I hate to say it, but I'm getting use to Vista for my gaming system, but I was very reluctant to use it just for DX10. Unfortunately, after buying a 2nd NVidia 8000 series card for SLI, the drivers are much better for Vista. It seems NVidia is also trying to push XP away (XP forceware drivers should be considered BETA as much trouble as they have).