Usually, the graphic subsystem (the
display manager, or DM) is started up as one of the last items in the
/etc/inittab file.
Exmples of DM's include KDM, XDM, and GDM.
If you cannot log-on graphically as root, it is because
the display manager has been told not to allow it. This is a configuration-file option that you can change.
But... you might not want to. You know, plenty of things are
easy to do in a graphical environment, and the computer will do
anything that root commands it to do, without waiting for ..
..
You have been warned.