for sins, assuming your computer IS a desktop I would suggest a LARGE cpu heatsink and then overclock the cpu to increase the GHZ, as sins is a single threaded application it only uses ONE of the cpu cores and benefits from the ghz far more than any other upgrade, and as you have enough ram the second choice replace the current ram (assuming dd2 800mhz/ddr3 1333mhz) with the fastest (highest mhz )ram you can fit, the third option would be the video card, but it is not going to affect the speed of the game much.

hope this helps

harpo

yrag, I have used a ati mobility 200 with sins without problems, and in my experience the biggest improvement is  cpu speed, the second best is the ram speed, and video card a poor third, and just for your info my primary development system (which I use for quick testing of maps/mods/etc has only a geforce 7600GS, and im my experence is cpu/ram bound far more than gpu bound.

harpo