The screen just shimmers for one or two seconds and than presents me again with the login menu.
This means that the username / password is wrong (KDE Why do you not just say so
, instead of "shimmering"?).
You will probably remember that login names and passwords are CasE SenSitiVE!
As none of these users have managed to log in, you could just delete them (usingmandrake control centre), and then start again (watch for the caps lock!).
If this fails, have you installed all the mandrake updates? There are many updates for 10.1, which you need. Please search this site for "Easy urpmi" and follow the instructions until you can do urpmi --update --auto-select
(as root). Then please try again.