Thank you very much, Storm for your nice and easy to follow answer!
You said that I should not use German Umlauts, yepp I would love not to do so Since it's an annoying pain, BUT I read in your first post that one should use the exact same user name and password as used for the Windows Box.
Since I was so smart to put Hans-Jörg there, I thought it might not work out with the user / password checking.
If all else fails I would have to change the windows install on my Dad's laptop I suppose
Thank you very much for your help again.