The Best game by far for Vista right now is Crysis..Un***believable...Crysis addict...
Vista has its qwerks like XP had its qwerks...I have had no problems with Vista Ultimate on my personal box.
With 3 gigs of ram you should be well above fine. Vista runs into problems with less then 1.5 Ram gaming wise.
Your PC will look like this if you play Crysis. Since you have vista and the nvidia 8800 you are DX10 capable.