What about
Filevault?
Even trusting the security, I've heard of all kinds of issues with that, including performance issues, risk of losing data, etc. And it wouldn't encrypt stuff in the swap file, temp files, etc.
And you can wipe the HD from the OS CD.
Not necessarily if the hardware isn't working right.
Alternatively you could call Apple and see what they say about this, they might be able to do something (i.e. let you go into the Apple Store with the technician to take out the HD if it went wrong).
I don't live anywhere near an Apple store