2gb of RAM would be good, but it won't come close to cancelling out the weakness of the video card. Trust me, I've tried it. The best you'll get to smooth, fast action place (with out the blinks and stutters), you'll have to downgrade all the graphics. Meaning you won't see textures, a bunch of solid blocks. I'd go in on an x700 system or higher if you really want to play that game.
Not saying that the x600 is super weak or anything, but it's just that game that it doesn't work well with it. It'll play WOW, DOOM3, and HL2 at very decent settings but it's just that one. I think when it loads up the world (it's giant, too much details), too much going on and very fast action gameplay. WOW- big world, but not that fast on the gameplay.