How do i fix my xbox live connection so that i wont lag out of every other game when I play Halo 3?

Almost every time i try to play a game on halo 3 i lag out right when the countdown to veto is about to end. I play gears of war and my connection is fine but when i try to play halo i cant even play 1game before my connection is lost and the "disconnected from xbox live" icon appears and i have to wait about five minutes before i can even sign back in. So I want to know how i can fix this because it's really annoying and makes me want to get rid of xbox live!