Been meaning to put this up for a while now. Dave got his Airport Express a few days ago and intergrated it into his setup at home. Thought I would do the same and compare the difference.
How to: Set up WDS like normal (http://docs.info.apple.com/article.html?artnum=107454), then stop the Extreme/Main Basestation from doing NAT and set the Express/Remote Basestation to a manual IP address on the same subnet as the rest of the network.
Resultn my PCs I run Windows/iTunes and GNU/daapd so I can listen to any and all of my illegal bounty throughout the house, and the xbox connects to the net for leet-o thumbnails and weather data, and streams films from a SMB share on said Win/GNU boxen.
Best of all: No holes and cables snaking across the length of the house
My setup is based around my hub which is a simple 10/100 8port hub. The smoothwall firewall protects the network just like in Daves network, but I also put personal firewalls on each workstation and laptop inside the network. I dont have to worry so much about wires because most of my setup is in one room except the wireless access point which sits in the middle of the house, so theres wireless in the garden. The xbox is my main mediaplayer, while I could use the video output on any of my workstations. Xbox mediacentre is too good specially teamed with SMB and XBMS shares on all machines in the network.