Harry,
Thanks for your response.
You guessed exactly right. I am going to be operating in a sensitive environment ( a lab) where i am introducing students to Linux and other open source softwares.
Unfortunately, I have no control over the hardware and as a result cannot really unplug disks or disable disks through BIOS etc.

The only option I have is really to use Knoppix and disable hard disk access. As you said, this isnt going to stop somebody who is really bent on hacking the machines.
But the school lab guys want me to at a minimum disable hard disk access in the Knoppix CDs that we hand out.