Connection problems with xbox live?

When i sit down to play xbox 360 using xbox live (particularly with Call of Duty 4 or Halo 3) my connection strength seems to fluxuate from being decent to being very weak. i experience a great deal of lagging and sometimes i am disconnected from games completely. I am using a linksys router with a password protected connection. i have 3 other computers connected wirelessly to my router- all Mac's, which are brand new and in perfect running condition.

My gameplay generally starts of relatively normal, until i begin to lag- which creates choppiness and sometimes a disconnection. could someone please tell me all of the different ways to optimize a connection and get the fastest gameplay possible for xbox 360? i am willing to try anything. I understand that disruption is somewhat common during internet gaming, but 10-15 interruptions a game finalized by a disconnect can't be right. please help!!