Set the default runlevel (in /etc/inittab, see the initdefault line) to 3 instead of 5, that should help. Runlevel 1, 2 and 6 are "reserved" (reboot, single-user and shutdown), but 2-5 are more or less normal runlevels. Usually 5 runs graphical server by default, along with a graphical login manager, and 3 doesn't - so it sticks to the console login. It may differ, though..
You change runlevels (in a booted system) with
you can try it and see if X shuts down, then you've got the right level. Don't do 'init 1' nor 6, as they're not ordinary runlevels. Changing the runlevel is done by editing (like I said) the /etc/inittab and changing the runlevel number in the initdefault line, then rebooting.
But if they couldn't log in, it didn't matter, and if they could, they could always run 'init N' to switch to runlevel N, thus getting to the graphical login.