MAC/PC troubleshooting problem

I currently use ATT for my internet service, along with the provided dsl router. We have 3-4 PC's that tie into the router via wired/wireless. There is also 1 MAC that connects via wireless. When nobody is on the MAC, our dsl works flawlessly. When the MAC is in use, the dsl router is constantly dropping and re-aquiring the signal. And since i am an avid gamer who uses a PC, this can be quite annoying with lag, constant DC's etc. ATT has moved our phone line to another circuit and replaced router so those arent the problem. Has anyone come across this before? any help would be appreciated

bump?