Hi, i guess you guys see a million of these threads a day, so i tried looking around first, but found nothing that helps

anyway...
I have a Netgear CABLE router RP614v4, for 3 months ive had no problems whatsoever running two PCs(XP sp2) with it, until recently a new flatmate joined the house and i offered to share some internet with him. He has a Macintoss running OSX, since he joined we've had frequent disconnects that last only a few seconds, but enough to disrupt gameplay and so on.
A 'Professional' told me to upgrade the firmware, i found there was a new release (Version 1.0.5_04.23) and downloaded and installed that.
From there things went to hell, The router stopped transmitting to the computer from the modem. Ive tried rolling back the firmware, restarting everything, run the setup wizard 20 times, changeing cables and everything short of smashing the router on someones head.
What can i do to get the router up again? any ideas? similar problems?
If i do get it up, how should i tackle the frequent disconnects?
Im no professional when it comes to networking, awnsers may have to be dumbed down some degree:P
if you need to know more specs, details, ill be hovering over this topic like a bee over honey laced with meth
regards, Phill