Get an MB that supports Athlon, a 1Ghz Athlon or better, MB should go around 100-120 for a pretty good one, CPU about the same.
About to upgrade my self aswell, will go for a MB wich supports DDR (266mhz) RAM and AMD CPU's, will keep my TNT2 for a while, works fine
Think the FPS will go up again though, will hopefully be fixed in a patch soon, I have about the same FPS as you have Dad, 10-15 in a msall fight, unplayable in bigger fights and when I black out.