I just ran into that same issue with an Actiontech modem/router... Qwest uses the modem for authentication, so it is extremely difficult to do port forwarding, or disbable NAT. I was told bt Qwest tech support that they didn't support that particular feature, and that if I wanted to do web hosting, I would have to use the bridging feature to allow everything to pass through (which if I understood correctly) was like putting it in DMZ mode, but still allowed the modem to do authentication. I wasn't going to pay Actiontech $45 for additional support, so I put it behind a different modem on a different connection.

I searched for two days to try and figure out how to get it to work and wasn't able to either... not real impressed with Qwest selling me a modem and then not offering full support for it either. That seems a bit underhanded to me.