Please configure your computer to get a static IP from the router first. Then portforward for that address. This will at least lower the possible causes of problem.
http://www.portforward.com/networking/staticip.htm Also, the zoom x3 modem seems to be also a router. The best would be to configure your lan IP as DMZ. Look there for more infos
http://www.askmarvin.ca/forums/index.php?showtopic=844
I'm not familiar as two bypass to routers... You'll have to do googling, but if you find the solution come back here to tell us please!
Bonne chance
