Blimey... you've not been using root? Well I guess you've filled in the password when requested...
Try su -
in a terminal/console (yes that's a hyphen in that command). You wont see the password characters echoed as *s when you type them but dont worry.
Now commands you run are as root.
To log in as root with a gui, you need to either use the KDE Control Centre to alter the Login Manager options, or use the MCC -> Hardware -> Display Manager to choose to use the KDM instead of the MdkDM to log in (You'll probably need to install kdm off the cds first).