Just use a crossover cable to plug the 2 xboxs together and you'll need an app to ftp between the xboxs. I really think though that the dashboard Avalaunch is what you should use as it have a built-in ftp server/client for xbox-2-xbox connections.
a good way of doing this is using belkin wirless adapters,the same thing as the cross over cable but no visible wires (pc world)