Concerning logging into Gnome (or any X setup) as root: that's not
recommended practice. Generally, you can override this safety setting by
tinkering in the Gnome configuration file (but I'm not sure of the
specifics, as I don't use Gnome). If you _must_ log into X as root (AND
YOU DON'T NEED TO!!), I recommend that you do it manually with "startx"
rather than allowing it from the login manager. Just start a second X
session ("startx -- :1", then Ctrl-Alt-F7 or Ctrl-Alt-F8 to toggle back
and forth between the two sessions) or kill the login manager first
("/etc/init.d/gdm stop").