I have seen a lot of posts on how to change your wireless internet NAT settings, although, I have a non-wireless Xbox Live setup. I have my Motorola modem, not wireless router that is plugged by Ethernet to the back of my Xbox 360, a cord that goes into the phone plug in at the wall, and the power source.
Look at the router and identify the vendor. Go to their site and access the support documentation. Generally, to access the router, you can do so by opening a web browser and typing the IP address in the browser's address field. When prompted type the username and password to get into the router's configuration.