Instructions
Connect the USB flash drive to a USB port on the front of the Xbox.
Scroll to the "My Xbox" tab. Select "System Settings."
Select "Memory." Select "USB Storage Device." You will have the option of removing all preexisting content on the flash drive and using all of the space for Xbox related content or partitioning only a portion of the drive for Xbox content. If you want to use the entire USB flash drive for the Xbox, select "Configure Now." If you only want to use a portion of the USB flash drive, select "Customize Configuration" and move the slider to select the amount of space you want to dedicate to the USB flash drive.
Select "Configure." The Xbox will test the drive to ensure compatibility. If the test is successful, the USB flash drive is ready for use. If the USB flash drive is rated below the recommended specifications, it will still work, though you may experience performance issues.