The WET11 is supposed to work as described, without drivers, etc.
Here is Linksys' page with an Xbox wireless setup. The only setup needed is done through a browser-based system in the device itself (its address is 192.168.1.255). You may need to alter your LAN, at least temporarily, to accomodate the 192.168.1.xxx subnet so you can configure the WET11, but you can change its address to match any existing LAN IP scheme you have, or set it to DHCP for automatic address assignment by whatever router/base station you already have.
Go to Linksys' site for the
WET11 for all the details. The documentation looks like it needs a PC, but with the browser interface to the box, you really don't.