u on pci-e gcard ? or AGP ?
might be worth you buying a new mobo that is more campatable with newr stuff, although ya aint gunna see an improvement now at least with yer next £50 or so better parts for cheaper money will be compatible

ya gunna buy upgrades for an old chassis............ keep the shit parts, just upgrade chassis first

like with motorcars

no point in wasting £100 for an increase in 10-15 fps thats gunna last about 12 months.
bite the bullit, and buy a newer mo-bo that runs both yer current gear and some better stuff