I thought I found a way to tackle this but things a getting stranger and stranger... I checked the md5 sum of the Knoppix 5.1 iso file and the md5 utility under windows generated the same md5 as in the md5 file.

When I boot Knoppix (in a PMI setup from hdd) and run the cheatcodes in the menue.lst script testcd and screen=800x600@75. There are no errors reported, no cloop, but two directories are missing - went two quick don´t know which.

Now the strange thing is that after booting the first time, the installation seems to work. After the second Knoppix start, the mouse does not work anymore, while i did not change anything Knoppix-wise. This is a complete miracle to me. An on and off error points to a hardware defect doesn´t it? Is the IDE controller defect? It seems to work under windows...