I run everything on the highest settings possible, everything enabled, anti-aliasing set to none, and resolution set to 1680 x 1050. I have no problems at all, never bogs down, and runs like a charm. Here are my specs...
Intel® Core™2 E8400 (6MB,3.0 GHz, 1333FSB)
Vista® Home Premium Edition SP1, 64-Bit
4GB Dual Channel DDR2 SDRAM at 800MHz - 4 DIMMs (using all of it)
SLi, Dual nVidia GeForce 9800GT 512MB
500GB - 7200RPM, SATA 3.0Gb/s, 16MB Cache