1 Gig should be plenty of RAM for most games.
2 Gigs is commonly considered the "sweet spot" right now because you never have to worry about Windows suddenly deciding to start hogging RAM for no reason. I upgraded my RAM and video card the same day (went up to a nVidia 7800GS and 2 Gigs of RAM) and I ran a series of benchmarks and usage tests when I was doing it. The video card alone gave me a major boost in gaming performance when I didn't have anything else running in the background, but the added RAM really helped out the most with "normal useage"stuff, like when I have a dozen or so programs running in the background while playing CS. The combination of the 2 is all sorts of kick-ass
