The FPS is fine.
What pings are you getting for the servers you join?
Does it matter how many people are in the server, does your connection hold if there are only 1 or 2 people? Is it worse when there are lots of people?
Make sure you're not downloading anything or have MSN, etc, running (obvious).
Are there any other other computers using your internet connection?
Any problems with other online games?
Do you use wireless or cable to connect to your router/modem?