No, Vista is not a good gaming OS.
Vista the OS by itself is average at best with at least SP1 installed, slightly better with SP2.
Win7 is where you need to be.
4GB or less than I'd run a 32-bit of Win7; if going 4GB or more then look into the compatibility issues and see about running Win7 64-bit.
I wouldn't even think about dropping back down to XP anymore
Win7 or get a mac.. (just kidding, no macs..)