mom needs help to connect xbox live, apple & alienware notebooks

Ok, my family has an xbox live (halo3 mostly) an apple & alienware (garrys mod mostly) notebooks. The xbox live is wired to the comcast wireless router right by the flatscreen tv. Problems are this...xbox live connection goes down frequently on halo3 (didn't do that when we had the modem that was not wireless) What i want to do is have the xbox live work correctly & still have wireless network for my computers. Do i need a different router? Do i have to separate the wireless router from the xbox connection? I paid comcast to come do this, but obviously they have failed & i am sure i can fix this myself if i just know what to do. If i went back to the comcast modem that just went into the xbox with the cable connection then the xbox will work, but then can i get a wireless router like the alienware gaming router & just plug it in elsewhere to power the apple & alienware laptops? The apple is brandnew & the alienware is a m5750. Please help me do this so i can regain my sanity... i am moderately computer savvy...not a geek, but i can follow instructions. thanks in advance. Sonja