Doesn't run okay as it is? With my new system I can play smoothly (30 fps min, 50-60fps avg) at 1680x1050, all high, 4xAA + AF with my 7800GT. I don't think RAM is much of an issue unless you got a ton of background programs running. As the person above me said, I only notice it for the close down time. Maybe it loads SLIGHTLY faster and whatnot, but when I had 1GB of RAM I didn't find it to be the issue. I went to 1.75GB and nothing really changed due to the RAM.
Of course, > 1GB is helpful for other games and apps and for how cheap it is, it is the better buy.