Oh man, this one sounds tough. I wish I could be sitting in front of the admin panel to poke around in it. But some thoughts:
Does your router have mac cloning? If you can turn off all of the routing capabilities of the modem/router, clone the mac address w/ your wireless router and push all of those duties to the wireless router, you might have better luck having one central location to set policies.
Another idea. Your modem/router probably has only 1 IP external address available and it is being used and pushed to your computer. Since the routing functions are being handled by the modem/router it cannot assign any others out so you have issues. By pushing that single IP address to your router ad then using your router to assign within your internal network, you might have better luck.
These are just shots in the dark but perhaps they might lead to something. Keep us posted on what you're trying and how it is going and hopefully we can get you to NAT 2!
