I've got Blueyonder and xbox live.
You go to the settings bit on your xbox (while there's no game in) and in one of the options there should be a MAC number written in the bottom left hand corner. it goes MAC-5568728 etc etc.
It's all here,
http://www.blueyonder.co.uk/blueyond...connected.html
I've not been on xbox live in quite a while. I used to play castle wolfenstein on it all the time.