I tried the cheat code knoppix screan=800X600@85 and than the monitor worked fine under Knoppix 5.0.
I tried the cheat code cdtest with my newer 5.1 cd and it found corrupt data.

I want to compare the image file with the md5 sums, so that I know whether the problem is with the download or the cd burning.

And I think that I will try a Poor Man´s Installation first. Maybe a way to get acqainted with Linux without the pressure of getting everything working immediately.

Thanks for your help.