Can anyone help with my Low FPS

i am running a Compaq amd k-6 2 533mhz and 312mb ram. The mother board haz an onboard vid card, I bought a Geforce 2 pci and tried CS and Diablo2 and get low Frames like 27 at high for CS and 18 at high for D2 with like 10+ skips. Is my machine not able to handle it? Those fps for ds are runned at Direct2d i believe and not open. can sum1 help me out?