If you have a version of KDE4 that does not allow you to enter into an administrative mode and configure autologin here is a command line version for this settings:
[X-:0-Core] AutoLoginAgain=true AutoLoginDelay=0 AutoLoginEnable=true AutoLoginLocked=false AutoLoginUser=lilo ClientLogFile=.xsession-errors
Add the above lines to the and of your:
/etc/kde4/kdm/kdmrc
file. The above example will auto login a user named "lilo" into a KDE4 system using KDM and a login manager. The AutoLoginDelay option specifies how many seconds a kdm will wait until it will execute a user auto login procedure.