With kdm@kde4, to add a KDE 3 session to the menu "session type" in kdm:
sudo cp /usr/kde/3.5/share/apps/kdm/sessions/kde.desktop /usr/kde/4/share/apps/kdm/sessions/
(And you can edit the line "name", of copied kde.desktop, from KDE to KDE 3)
This KIND OF works, but now kde3 runs with the kde4 base (I think) and it both broke the start menu and Tasma for the user that logged into kde3 PERMANENTLY!
This user is not shown any Tasma modules anymore, the left hand column remains empty and thus the user cannot configure kde3 anymore, not even when switching back to kdebase!
Please tell me how to fix this! Re-installing Tasma is not an option, as it is in the userfiles, but I don't know where... For other users who didn't log into kde3 from kde4's kdm, Tasma still works...