Uhmm.. Aside from toning your graphic settings ALL the way down (like I do), removing all the 'effects' like the casing drops, bullet marks, and even the blood settings will help.
Actual video card settings in windows will help too. If you have a 3d driver, make sure you set it to 'performance' and not 'quality'. Use 16bit color, not 32bit. (not that this really matters, urt will force 16bit color if you tell it to.)
Thats about the extent of my knowledge. Much past this, you'd better beg pyrite for some help.
oh, & remember "a change imposed, is a change opposed'' -who moved my cheese