How to Transfer Your Gamertag to Your USB
- 1). Insert a USB drive into a USB port on the console, and then power it on. Go over to System Settings on the My Xbox menu, and press "A."
- 2). Choose "Memory" and press the "A" button. This opens a Storage Devices screen. Highlight "All Devices" and press "A." This opens the contents of your storage devices.
- 3). Select "Gamer Profiles" and push your "A" button. This exposes your profile. Highlight the profile, and select "Move." This takes you back to the Storage Devices list.
- 4). Highlight the "USB Storage Device" option at the bottom, and press the "A" button to transfer.
- 5). Remove the USB drive after the transfer completes.
Source...