Things You'll Need
Instructions
Remove any external hard drives already connected to the Xbox 360 (either via USB or via the console's SATA hard drive port on the left side of the machine). Plug the hard drive you wish to use with the Xbox 360 in to a free USB port on the front or rear of the Xbox.
Power on the console and wait for the main menu or "Dashboard" to load. The system will detect your hard drive automatically and ask you if you want to format it for use with the Xbox 360 as a USB storage device. Press the "A" button on the controller to reformat the hard drive (this will erase all data stored on the hard drive before the reformatting).
The console will restart and load the Dashboard again. Your USB hard drive will be formatted for use with the console and can be accessed as a storage device within the "System" Dashboard tab under the "Memory" option.