Thanks for the detailed answer and the advice! Yes I put it on MBR! Of course I won't consider removing knoppix, it's great!

The windows partition I only had for experimental purposes, it seems illogical but one thing I have learned with computer problems that at some point one has to try out all sort of crazy things - the result can both be monstrous or nice, just like evolution...

Now I have made a third Linux partition out of it with Qparted. Filesystem is ext3 according to Quparted. I also considered it to be a bug of the installer, but since Qparted keeps giving me error messages about "strange filesystems" it's definitely something with the harddrive. I would reproduce the error-messages if I could, but at the moment I dont dare to fiddle around with it... I will do that with the floppy and e2fsck though...