This will give you an idea of how BFBC2 will preform on your current PC, as long as you know what graphics card you have and can mentally adjust for your CPU. Unless you've already bought the game and have figured out you probably need to upgrade. I think I would get around 30FPS on low settings with my 9800GT and P4 3Ghz w/1gig. But low is real ugly.
http://www.techspot.com/article/255-battlefield-bad-company2-performance/Gomers 8800GTS doesn't look good.
Gomer you got the CPU go buy a Radeon HD5850 or 5770.... damn prices have gone up, or should I say the dollar has gone down. Crank up the video settings and be awed by the difference. Supposedly they've optimized the game for a threaded environment so quad cores will have a nice boost.
Also, Stalker Call of Pripyat will use all your cores if you alt tab out of the game, open your Task Manager, right click the xrayengine.exe (or something like that), select the Select Affinity tab, and check all your CPUs. I haven't checked this to see if it helps on a single core using hyperthreading but it would be worth a try.