Aha, a Wireless bridge device. It's starting to make all sense now. I'm sorry that i didn't see that earlier
First of all, did you upgrade it to the latest firmware available?
It's not working at all now, right? Then i think it's best to get it back to its factory default settings. See the manual if you can do this with some kind of little button on the device itself.
Your WGE111 is capable of 54Mbps at max. So make sure you have a Wireless-G network (802.11G) enabled in your wireless [b]router/b]. That wireless router is either built in your modem (your modem has antennas) or directly connected to your modem. I sure hope its builtin, because if it is not, it will make things more difficult. Also make sure your wireless router accepts new incoming wireless devices (after it all works you can disable this again). Usually you can configure all this inside the webbrowser configuration page of your wireless router.
After that, try the configuration utility. You will probably be required to connect your WGE111 to your computer via a UTP cable for a while. See the manual for more information. It's probably accessible at some ip adress like 192.168.0.1 or something. Your network interface card (NIC) inside your pc might need a static ip address for a while.
You should be able to connect it to your wireless router by searching for the correct SSID (your wireless router) and typing in the correct passkey.
Then you need to open up a few ports on the device in order to have a good Xbox Live connection.
If you can enable uPNP inside both the wireless router and WGE111, then use uPNP instead of opening up ports. The Xbox 360 is uPNP compatible. I am not sure if this will work as it should be, because i don't know if the uPNP information is also "bridged-along-wirelessly". If it fails, open up the ports as described below instead:
The Xbox Live service uses UDP ports 88 and 3074 as well as TCP port 3074. Should be open for both in and outbound communication.
Next, check if those ports are also open on your wireless router as well.
Next save all the changes and make sure the WGE111 can find your wireless network perfectly.
Then disconnect it from your pc and connect it to your inactivated Xbox 360. Next power on the 360. Check your wireless router if you see the WGE111 connecting to it.
If this all works, secury both your router and WGE11 device. Change the admin/root passwords to something other than the default password. Do not allow new devices to connect automatically to your wireless network as well.