Well, you see, in order to run games smoothly, I believe that you need a lot of video card RAM, and a lot of system RAM.
I suppose getting something like a 9700, or Nvidia 4600, 4400 128MB cards will give you one hell of a kick in graphics performance, but, while running a game, you will need to insure that you have a very limited amount of programs running in the background, the less the better, otherwise, you're going to experience slowdown, and more.
If you're willing, go with a newer graphics card. However, it would be much better, to go with both.
I'd go for more RAM mate. I have a 8500 not latest but certainly not a shaby card, anyway when playing stuff like UT2003 and more graphic intensive games i wish i had more RAM, an extra 256 RAM would make a heck of a difference.