I've played a fair amount of games under Vista (BF2, BF2142, C&C3, FEAR, HL2:EP1, Supreme Commander. Doom3, Prey) and overall the performance has been fine. The ram usage is only about 200 MB more than XP and with games like Supreme Commander, whether I play under XP or Vista, I still hit around 85% memory usage.
The OpenGL games are about 15-20 fps slower than under XP, but I'm still in the 100s, so it doesn't really matter.
BF2 seems to occasicanlly have this problem and I think it ties in to the Superfetch feature, where it will start stuutering really bad for about 15-25 secs. When I watch the new Resource Monitor, it shows that the Common_Client.zip and Objects_Client.zip. are being read fairly heavily. I'm not sure if this is because of punkbuster or not, as I don't get it everytime I play or on every server. But it only happens every so often, normally at the start of the map. I played for about 2 hours straight one night and it happened about 5 times, with the longest time being around 1 minute, annoying, but hardly a show stopper. Funny enough, I've played BF1942 and 2142 and I don't get that.
Personally if I was you, I'd wait a little longer, since you have a nVidia card. nVidia drivers are still struggling for some people. So you might play perfectly fine or you might fine that your game(s) are having issues. Tiger Woods Golf 2007 seems to be one of the worst one. Different people in the FEAR forums report different problems\results.
I have an ATI card and so far, the drivers (except for the 7.3s) have been great. Looking in the EA forums, the people who can play TW 07 are the ATI owners. Though it does seem most of the really bad problems are with the 8800 series. I have a 6800GT system and haven't seen any issues so far (though I don't game on that system as much).
Anyways, back to your main question. 2GB of ram is still fine for gaming, even under Vista. In the big picture, the memory usage isn't that much different than XP
Side note, I triple boot between Vista32, Vista64 and XP32