One more time --- you're in the wrong forum for hardware and settings advice! Start reading the AVSIM Hardware forum.
I've posted in the Avsim hardware forum, but it can't hurt to ask here, too. I've gotten some good advice.

Do you use woAI? I have UT2, a friend got it for me, but now I want world of AI, because UT2 has low amounts of AI.   And also I have good frames, and it's a 2GB of RAM computer!  I don't know you're problem though.....
For whatever reason, WoAI did not work well on my computer--I think it was the FS9 .bgl files screwing with my system.  :-/