if you is asking how to login as root in the graphical mode, beggining from the login screen, this is not possible to make from KDE, only from GNOME, but....
you will not becomes a root user, but a system root....!
is VERY DANGEROUS to your system this procedure!
ALBERTO FEDERMAN NETO
Favorite Distros: Sabayon, Gentoo, Mageia and OpenSUSE