I spent days trying to figure this out on my old netgear modem only to find out it was impossible.
Anything you could need to do that's helpful is impossible on a netgear...
Yeah i know, that modem was one the ISP gave me for signing up for an account and at the time i did not know anything about modems and features. I was happy the day it blew up so i could something better. After much debate with those who say they know i bought a linksys, it runs fine, better connect speeds and downloads, but its an impossible heap of crap to configure to do anything simple, i want to port forward 8000 to 192.168.11.x the tap connection, but the config will only let you forward to 192.168.1.x which is the local network.
So i change the local network to use 192.168.11.x and windows craps out as soon as the tap configures, it would seem that windows is rather particular about the ips running on the internal network, 192.168.11.1 and 192.168.11.150 for the tap, 192.168.11.30 for my machine and 192.168.11.11 for the gateway, but it falls apart somewhere and im not sure where yet.
So if you can understand my gibberish you have done well, in summery, you will need a modem that allows you to forward to the tap IP and not only to the local network.