I have an Athlon 64 3200+, 1 gig of CorsairXMS ram (CL 2), Gigabyte K8NS motherboard (n-force 3 chipset), Audigy sound card and a heat damaged ti4200 vid card atm.
In game settings: 1024 x 768, 512 textures, preload textures and skins to system memory, AA x 2, vsync on, others skins on, weapon and gv effects on, mipmapping, transitions, horizons on, detail sliders are at default settings, none more than halfway to the left.
I have seen fps as high as 159 (with vsync off). When OzKansas was up even over Furball Island with scores of gv's and planes I never saw a slideshow. (Once I even forgot to turn off all back ground processes and didnt notice any difference in game play) Most of the time my fr is pegged at 85 (monitor refresh rate), the lowest I have seen it go is 36. When I attempted to turn AA up to x4 I saw a pretty big performance hit and my fr would drop into the mid 20's at times.
Before I upgraded I was running an Athlon 2000XP (1.66ghz) and 512m ram, I had extreme difficulties running the game at acceptable frame rates. I had turned all video options off or as low as they would go and still couldnt maintain acceptable frame rates.
Humble with your rig you really should be able to run the game with very good fps AND with alot of the eye candy turned on.