Goodness, dlh! What on Earth are you doing resurrecting an old topic? Was the post misplaced?
Anyway, seeing that it's been resurrected I'd like to add comment related to the original question. There is really only one way to ensure beyond doubt that another person does not use your PC. Install a removable drive cradle to your PC, mount the hard drive in it, and then whenever you shut the system down remove the hard drive from it! If there's no system drive in there the PC cannot be used!
http://www.addonics.com/products/external_hdd/combo_removable.asp
http://www.addonics.com/products/mobile_rack/aenrhdsa35-r.asp
Password protection is not adequate protection against knowledgeable computer users. Password cracking tools are freely available for download if you know how to look for them ;)