After you download the Ubuntu ISO and burn a live-DVD you can boot the computer without writing anything to the Windows hard drive. Just install Ubuntu on the external Hard drive. No need to open the computer and physically disconnect the Windows Hard drive. I use a 4-gig USB flash drive with the desktop edition of Ubuntu on my Lap-Top. There is no hard drive in the Lap-Top at all. I keep the flash drive around my neck when the Lap-top is not being used. If the Lap-Top is stolen they get no information or data.