Opengl, Windows 2000 and Geforce 2

i have serious problems palying Quake 2 with my Geforce 2 MX (Hercules 3D Prophet II MX).
When I set cl_maxfps more than 30-35 the game freezes. I have Isdn and normally the correct rate and maxfps are 5000 and 90-100.
More, when I set to 30 maxfps, I have problems of Lagging… What can I do?