How to Connect a Portable Hard Drive to an Xbox
- 1). Plug your USB memory device into the Xbox 360 console. Turn on the Xbox 360 and allow the system's main menu or "Dashboard" to load. You will use the Dashboard to format your USB memory device for use as an Xbox 360 hard drive.
- 2). Move the Xbox 360 analog stick to the right and select the "System" tab in the Dashboard. Press "A" and select "Memory." Press "A" and select "USB Devices," then select "Format." Press the "A" button again and the Xbox 360 will begin formatting the USB device for use with the console.
- 3). Wait for the formatting process to complete, then turn off the console. Turn the Xbox 360 back on again and the USB device will be connected as an external hard drive for use with games, movies, music and photos.
Source...