If you want to try trace repairs on your original Xbox this post
My last answer was a bit short (too busy watching the F1 GP!!). You can also do the unlock / lock on your Xboxes. Unlocking the disk is easy - just run Config Magic or Evox Dash on your broken Xbox, and select the unlocking option.
Relocking on your new Xbox is a bit more involved, but not much. You need a second power source for the replacement hard drive, then you use Chimp 2618 (burned to DVD-R at 4x or slower). Get everything set up, boot with chimp, hotswap the new disk onto the DVD IDE connector, then just select the chimp disk locking option.