If you can't update your video drivers, have you installed the latest patch for UT?
Correction Uber Neuman, if your overclocked system is truely stable then UT won't be a problem. I have a PIII600@800 and it runs UT perfect on W2K. Now I have a PIII650@910 and it ran everything perfect EXCEPT UT!! So I dropped it down a notch to 865 and it runs perfect now. What that was telling me is that my system wasn't TRUELY stable at that speed. 😉