A google search yeilded this javascript for disabling the control key and right click. If it works, you won't be able to get out of the kiosk:
http://www.weberdev.com/phorum/read.php?f=7&i=42&t=42

Another thought: you could get a cheap keyboard and mechanically disable the control key somehow.

The knoppix cheat codes are typed in at the knoppix boot prompt as in:
boot: knoppix desktop=wmaker noeject
You can build them into a custom boot floppy or knoppix cd as described on our Knoppix Tricks page: http://www.cclug.org/wiki/Main/KnoppixTricks

You are welcome to the help. Your project got me setting up a knoppix kiosk which I had not tried before; and now I can show it to our club.