Quake 3 Freezing

My Quake3Arena keeps locking up on random parts of the game. In the menu, changing maps, or durning play… Sometimes it’s frozen and then unfroze like 30sec. latter, it’s almost like I’m really lagged, but it happens everywhere in the program.

My system is this:
Dual Pentium III - 733mhz
384megs RAM
Win2000 Pro.
Matrox Millenium g400 32meg