Originally Posted by GrouchyAdmin

Hold down F12. Choose 'USB'. If that's not an option, press F2, go into the BIOS, and enable USB boot.

If the HD isn't bootable, it won't work.

I doubt Windows will work, anyhow, since it was setup for a different machine which likely has entirely different hardware.

Your best bet would be to connect the HD and use a ghost utility to back up the internal drive to the external.