My machine 1.300mhz amd athlonxp, 700 ram, gforce5200 128.
I get same FPS with low and high details.
If I change options nvidia does not improve.
Start the game with 1024 resolution 80-90 FPS, with 800, 90-100 fps.
I can try omega drivers or gameboost or gameaccelerator, but i think will not better work.
P.D. Sorry for my english.