Could also lower your desktop resolution which determines your game resolution. Also, make sure that your anti-aliasing and anistropic filtering are off on your video card. Make sure that you don't have any programs running in the background as well. And as with any game that you have trouble playing due to low fps, reboot before playing so as to maximize the available resources that your system is able to allocate to run the program. On my old system, i had to reboot every 30min or so to play Morrowind, as i would run out of RAM. Just so you know, memory is the cheapest, easiest, and generally the most effective upgrade you can make to an older system.