I only tried Vista for a week and I had problems and had to revert to XP. But I am given to understand that most games can be made to run on Vista in compatability mode if they won't run directly and of course there are a handful of new games out that are Vista only. They will not run under XP at all. There are complaints that your framerate takes a hit under Vista though, it does slow the graphics card up, not a problem if you have decent graphics but mine is rather basic by todays standards and as such I think Vista would make many games unplayable on my PC at the moment.
I would try the games you are on about first, see if they will run and then make your mind up.
Just a comment about gaming and FRAPS on vista, I have posted recently on being unable to play MOH airbourne at times, with "all" settings "on low" FRAPS shows an average of 120FPS but down to 1-2 FPS at times and nearly stops altogther and usually does it at basic parts of scenery, with nothing really to tax it, and I found I was not alone...
Bioshock however works flawlessley with all settings up high, and so does the Crysis demo........ not sure of FRAPS though just know it looked very smooth in gameplay.
Vista Premium, E6750, 640MB 8800GTS, 2GB RAM........
That most games can be run on Vista with a bit of tweaking...(usually involving admin rights) I have Max Payne 1 (released for win98 and patched for xp a year later) Max Payne2, Doom, Quake, to name but a few. When you first try to install them, UAC bleats like mad, but they run fine with minor tweaks.
Some games have been reporting low frame rates but this is a driver issue, and is gradually being addressed.
I think the best advice is to search the gamers sites for details on specific games, If you want details on any of the above, you an email me via the envelope. :)