Performance: Games like Battlefield 2 already have a hefty memory requirement. While they will play under Vista, I recommend 2 gigs of ram minimum. I don't recommend anything less than 1 gig.
Drivers: while this could go under performance, it is such a big deal that it rates it's own section. Vista shipped with a decent base set of drivers. No it doesn't include everything. No, they don't support the advanced driver features we like. Companies like Nvidia are having to completely rewrite their driver code to be Vista compliant. Update your drivers to the latest versions. If that doesn't solve your issue check back in a few weeks and update again. Many places offer email notification when they release new drivers.
If you have specific game questions, please post in the games forum. I'll be glad to assist.
Thanks,
Starjax