You have to spend money on a decent graphics card or forget the good frame rates.
Your mainboard is almost without doubt, limited to 4x AGP bus speed and not 8x AGP.
I can only recommend that you search for a good quality 4x AGP card such as the XFX GF4 TI4200 64mb ($80)or get a better GF4 FX5600 128mb 8x AGP ($90) card of similar quality that will run at 4x AGP and will be of some use if you upgrade your PC.
A cheaper card such as the FX5200 isn't going to do the trick.
look here for U.S. prices on the various video cards for some bottom line pricing to compare your prospective purchase with.
www.pricewatch.comWhat? no money?
Well, if your current video card is 32mb and it's onboard video, go into your bios setting and switch the shared video memory to 64 mb and get yourself a free 64mb video card!
(if you can spare the ram..)
Mainboard: Asus P5K-Premium, CPU=Intel E6850 @ x8x450fsb 3.6ghz, RAM: 4gb PC8500 Team Dark, Video: NV8800GT, HDD: 2x1Tb Samsung F3 RAID-0 + 1Tb F3, PSU: Antec 550 Basiq, OS: Win7x64, Display: 24" WS LCD