thats a good framerate with your card. the thing is, ut2k3 automatically detects your system settings, and it selects its own resolution/texture quality at default. however if you select the same settings, a gf4ti4600 would make an extremely drastic difference from a gf3ti500. i'm not exact on the numbers, but you can easily expect 20-30fps boost in certain areas.
Athlon XP 1.58GHz | MSI KT3 Ultra2 | 256MB DDR PC-3000 | GeForce 4 ti4200 64mb @ 310/533 | IBM 120GXP 40.0GB | Det. 41.09 | DX 9 RC2 | Win XP SP1