This is a simple way to add an onscreen keyboard to KDM. This should be helpful for users who cannot type using a physical keyboard but can operate a mouse or touchpad.
Step 1: sudo vi /etc/kde/kdm/Xsetup
Step 2: add xvkdb & to the last line of /etc/kde/kdm/Xsetup
Step 3: save /etc/kde/kdm/Xsetup by typing :wq
Step 4: sudo vi /etc/kde/kdm/kdmrc
Step 5: change UseTheme=true to UseTheme=false (on line 443)
Step 6: save /etc/kde/kdm/kdmrc by typing :wq
That should do it. You will loose the regular theme settings. Due to bugs.