a) knoppix and debian aren't the same.
Knoppix is meant to be a boot-from-cd system, but knoppix is a debian-based system, afaik.
For installation I would suggest the debian.
Else you allways get the same hardware redetected, configuration-files overwritten etc.
If you have the same dvd as I have, one side has the knoppix-boot system, and the other the debian-install system.

If you're going to install the knoppix-system, there should be a hd-install or similar called script.

Perhaps you need to create a filesystem on the second hd fiirst.