Yes 2gb is good. I have a slow DDR 1gb ram that plays all my games. CoD5, RA3, L4D, WC3 everything!
4gb would be the BEST for games, but 2gb will do you fine, unless you want to a bit further then 2gb is good.
For games though it's mainly the Graphics Card that matter. I have a 7600GT that plays all my games as I said above and it's fine. Yours should be fine too, though I don't think you can play all your games on Max settings. But normal, which is good enough.
If your a hard core full-time gamer, then get a 8800, 9800, HD4870 or HD4850 with 4gb RAM and atleast 2.2ghz.
But for normal use, your fine