This is my setup. I bought a $35 WRT54G V6 wireless router at Walmart, it was on special, but you can find these deals around the net. I had a Vonage VWR wireless router because I use Vonage, but that could be replaced by a second $35 wireless router.
The VWR is the internet gateway and remains the way it came out of the box. (Except for the password and encryption of course.) The second router, the WRT54G, I reflashed with DD-WRT. DD-WRT is a freeware firmware that allows you to put the WRT54G (and many other other wireless routers) in client bridge mode.
I plugged my Xbox and Xbox 360 via ethernet cables into the ports on the WRT54G. DD-WRT routes all ethernet traffic via the wireless ports to the internet gateway.
This setup eliminates the need for a $100 adapter for the Xbox 360 and a $75 wireless bridge for the Xbox.
If anyone chooses to do this and needs some help, just ask.