Instructions
Turn off your Xbox 360.
Unplug the hard drive's power cord from the wall outlet.
Connect the USB cord from your external hard drive to any available USB port on your Xbox.
Plug the hard drive's power cord into the wall outlet, and turn on your Xbox 360.
Go to "My Xbox" on the dashboard. Select "System Settings," and press the "A" button.
Select "Memory," and press "A."
Select "USB Storage Device," and then press "A."
Select "Configure Now," and then press the "A" button. This loads a confirmation dialog.
Select "Yes," and then press "A." The console automatically formats the drive for use. The drive will now be selectable when saving data from your Xbox 360.