Yeah thats right, if i understand it correctly he is connecting the xbox to his LAN connection and trying to use the Wireless connection to connect it to the internet. If i have that correct there is probably a better way to do it. I have done this previously by:
1. Removing the interface bridge
2. Enable ICS on the wireless adaptor.
Internet Connection Sharing - Enable.
3. Set the local area connections gateway to the IP of the wireless connection.
4. On the xbox set the gateway to the local area connections IP address.
I could be totally wrong about how he wants this set up, wont know much more until the OP posts further details.