You actually need a pretty beefy machine to run that game. You seem to have everything else good, but even to run quake 4 decent, a friend had dual Geforce 6 6600GT cards in SLi mode, and that could handle it ok.....
If your board can do SLi, then id recommend just spending alittle over $200 to buy two 6600GT PCI-e cards and rock out. :-)
