this is it. /etc/passwd looks as follows:
this i changed now to:
and it works. there are a few lines of error printed, but i got sudo.
i will see now to get login working, and then to reconstruate all this on another clean system to make sure i can do it on my own.
i also ordered now an expresscard reader to make all this more convenient.
i am already very pleased with the result, and again thankful to you for working on this with me.