OpenGl or Direct 3d? Please help....

This is a 4+ month problem. My Nvidia Geforce 256 64mb on my winxp 1.5ghz machine has some WEIRD memory leak problem. When ever I play games like MOH, Jedi Knight 2 and others my PC runs like crap. Anyone heard of this problem, I have tried past drivers to no avail…thanks so much guys!