Several of the posters have touched on this, but it is so important that I wanted to make it a seperate post. Physical security of your computer (controlling physical access) is the first and basic step in defending against knowlegable persons. I have never been able to absolutely deny access to a person with extended, unobserved access to a computer. If a person can add or remove hardware, reset your bios password, add and remove drives, etc., it's really hard to protect things. In fact, if you have something a competitor or a spy really wants, they can just walk out with the whole computer if there is no physical security.

Szafran -- it's not that your information isn't potentally of some use to some, it's just that most of us have, for really important computers, provided physical security, prevented boots from external drives, password protected the bios, selected an operating with significant security features, and implemented those procedures. For these reasons, the things you propose won't work on computers we care about.