Just thought id share my thoughts with you all and maybe a little advice if you dont know already.
I'm an IT technician and have worked with wireless for about 9 years, one conclusion i have come to is that its unreliable but hey if you have to use it then read on!!
So ive been happy that my xbox360 has been joined to Live using my trusty cable, however a few weeks ago i decied to move the thing upstairs to the spare room. Shit!! didnt think about the lack of internets upstairs!! So i looked about on the net for a wireless dongle....£50!!! for a wireless adaptor!!! You have to be mad to pay those prices!!
So i have a soloution and its not run a 15m ethernet cable but does include a laptop with a wireless adaptor.
Make sure your laptop is connected to your wireless router, now plug the ethernet cable from your xbox360 into the laptop. Now right click on my network places and click properties(if there is no 'my network places' on your desktop you are probabaly using the shitty WinXP theme, shame on you!! you will have to venture into the control panel).
You should now see your two network cards, wireless one, and the ethernet one. Highlight the two by dragging the mouse while holding the left mouse button or using the Ctrl key and clicking. Once highlighted right click on one of the connection and hit bridge connections.
Right after a moment or two they should be bridged, like me you may need to disable and 3rd party firewall software and turn on the windows one. It should now work, hey presto a wireless adaptor for nothing!(if you have a laptop) (excuse my spelling)