Ok, I think I got it (have your TV and 360 on while doing this)
-Go to Airport Utility
-Manual Configure
-Internet Icon
-DHCP Icon
-On the bottom you'll see a + click it
-It will ask for Description, I used Xbox 360
-Reserve address by MAC address should be highlighted under it
-Click "Continue"
-On this page you will put in your Xbox's MAC address (why your TV and Xbox should be on) under configre network, on your 360, go to additional settings and advanced settings, there you will find your "Wired MAC Address"
-back to airport utility type your MAC address in there and pick a IP for your Xbox to be assigned.
-After this your still under the "internet icon" on airport utility click NAT
-click "enable default host", this is where you will put your Xbox's assigned IP you just gave it.
Doing this will assign your Xbox a IP and put all major traffic to it FIRST, kinda like priority over all network traffic, where you want it anyways. Email me if you have any issues, I hope I can help a few people out.
-Paul