I am no networking expert, but I have dabbled enough to feel your pain Saint.
I googled your modem and here is a link to the user's guide (pdf):
http://broadband.motorola.com/consum...User_Guide.pdf
You might want to look for info on the DMZ (demilitarized zone) and port triggering/forwarding. Maybe you can find some clues there.
Hope that helps until a network guru comes along.
