I successfully added a usb hard drive to my 40gig ATV. My internal hard drive is pretty full. Is there a way to transfer some of the movie files to the new usb drive?
If you have AFP installed, mount both the internal and external drives on a networked Mac. Then copy from internal to external; and when you are satisfied that the copy is complete, you can delete from the internal.
If you do not have AFP installed, you can use Cyberduck to accomplish the same result.