thats an agp card if I remember correctly, try looking for a ati 9800xt card, has alittle more punch! or if your mobo will support it, an nvidia 6800gt which I happen to have a working one, I may be willing to part with.
those older mobo's usually accept either ati or nvidia cards.
also check your memory, you want to max it out, prolly 2 gigs thats typical on the older agp mobos. that will ensure your processing is opened up as far as you can go aside from over clocking.
also check to see if you can put in a better processor. used parts for an older system like you have are real cheap, about 200 bucks, no more. otherwise you just over haul the whole system for about 1300.
so look at your cpu, your memory size and search around for a 9800xt ati or a nvidia 6800gt.
those will help marginally without getting a whole new system.