Chup- Try bumping that AGP aperture size up to 128 if possible, or at least toy around with the aperture settings to see if you get better performance. It may be meaningless, but is probably worth a shot. Like the others said, another 256mb of ram would help for sure- across the board. Good luck.
Kev- Right on. GF3s still rock. I'm not saavy enough to know the details, but I'm under the impression that Unreal 2 and Unreal Tourney 2003 use different engines (or different versions of same engine?)