What kind of internet do you have, DSL?
There isn't much to do, if the xbox is in the dmz and all your other computers can connect fine it's unlikely to be an issue with the router.
There is no way to open a NAT touble on most routers, it is what it is, and the NAT on these routers are open.
Lots of people use XBL and play games online without ever having to forward a single port, but with your xbox in the dmz, again it's unlikely to be a router problem.
If you have DSL there is the possibility of double NAT though, which is what you're problem could be, it depends on your ISP and the model modem they gave you.
Message Edited by Jason on 03-29-2009 10:59 AM
Message Edited by Jason on 03-29-2009 11:00 AM