I doubt this is the way you have it setup, but I have my main AP Ext. BS setup and my express is connected wirelessly using WDS...from my express, I am connecting my xbox to the 2-way enet port on the airport express. I have everything on my lan configured with static ip, but if you are running everything off of DHCP using the airport, then it should essentially be plug and play...turn on the xbox, the AP express senses that the enet port is being used as a bridge, and voila! If everything suddenly quit running however, try powercycling your network...start turning everything off beginning with the broadband modem, then any other routers/switches you might be using, then the airport express, then the xbox...leave is set for a quick 5 secs, then go in the same order to power everything back up...Routers are crazy sometimes and just need to have the power cycled on them...Hope this helps!