basically go to the xbox website and try to login there with email addresses you can remember. If you still cant remember call xbox support over the phone and they can tell you or change that email address after you answer questionsa bout the account like name, address, etc…
http://support.microsoft.com/default.aspx?scid=kb;en-us;906932&sd=xbox
http://www.xbox.com/en-US/support/connecttolive/xbox360/livesetup/recovergamertag.htm
