Multiplayer unplayable

So I finally managed to get into a multiplayer server, and any server I join my game freezes for a couple of seconds with almost no break between freezes. It is allowed as trusted in my firewall, all network traffic from the game is not being scanned.

VISTA SP2,
CORE 2 DUO E6420 2.13GHZ per core
2GB DDR2 RAM
9800GT OC