Why modem has a problem with xbox live?

I have Netgear CG814WG v2 Gateway and i always try to play Halo 3 but when im playing and IM IN FIRST!!!!! IDK i just get knocked off and get -exp. If someone could suggest a new modem that you use or that will no knock me off ASAP. I need a good price maybe 50 bucks cuz ima try and buy it today so i can Pwn some noobs.