I'm struggling with this problem myself. Not reached a resolution yet (diallup sloth).

What I do know is that

a re-install from the Knoppix CD put me back to square one
is true. Unless you have a seperate /home. When it's less true.

http://www.knoppix.net/forum/viewtopic.php?t=4051

for details.

One thought: if you did nothing and your Kde is goosed, it might be possible to recover.

Thoughts, anyone?