It worked ;-) I had to fumble a bit to get LILO to work with my harddisks, but I found a helpful description over on the Knoppix Formums that did the trick for me…

More small things that needed fixing:

• Can’t access my other harddisk as non-root

Fixed:

• sound is garbled in hd-install, works fine when booting Knoppix from CD
  add “alsa” to the linux kernels boot options