I'm a first time poster too, but I saw this problem and I had to respond. I had seriious framerate issues with this game until I did this:
1: Go into your ut2004\system directroy
2:Open up your ut2004.ini file in any text editor (After having backed it up first, obviously.)
3: Find the line VARSize=32
4: Change it to VARSize=64
Enjoy a slightly less choppy gamin experience. this changes the amount of agp memory the game can use, or something along those lines, anyway.
For obvious reasons, it's best only to attempt this fix if you have more than 64meg of video memory.
Sam B