I've got a MAC as well and pretty much from the moment I plugged it in, I've had wireless problems. I've tried getting the problems worked out at the MAC forums, but NO SUCH LUCK. A ton of users have difficulty with their macs/wirelessly connected. My other machines, that are wireless, do not have the same problems as the mac. I would be more inclined to blame it on the mac wireless adaptor before blaming the router. This is just based on my experiences/problems with the mac system, I'm not saying that this is causing your troubles, but it at least warrants further investigation.
I finally got so tired of the mac giving me troubles and not being able to get anyone to help me out in the forums, I just gave up on the mac and all I do with it is keep the OS software updated on it. Pretty much a $1600 paper weight right now. Hope you get your problem worked out. If it were me, I would try using the ethernet connection and see if the internet interrupts/disconnections stop. If they go away, then you know it is probably that notorious wireless adaptor bug/problem that Apple cannot seem to get right.