Geforce3 Ti 500, and Counter-strike

Hi, i have a P4 1.6gig Dimension 4300, 1gig SD RAM, 64mb Hercules GF3 Ti 500, 40gig HD, and a 17" Trinitron P792(running at 100hz in-game). When i play counter-strike, i get up to 100fps no problem. But when action starts happening, and i get into fights, i hit 50 or so VERY easily. My mouse moves 2 pixels at a time intead of one, and my graphics skip approx. every second. I was wondering if an OpenGL problem could be the cause? if so, what should i do to fix it. I am currently running the newest Detonator XP video drivers from Nvidia.