GDM is installed.

Do _NOT_ use /etc/ttys to start gdm at boot time.  This will result in gdm 
hanging or restarting constantly.  Instead, copy the included gdm.sh.sample 
script to gdm.sh, and restart.  This script is found, by default, in
/usr/X11R6/etc/rc.d.

GDM uses its own locale.alias file to determine its language and especially
the GNOME-2 fontencoding. This file is located, by default, in 
/usr/X11R6/etc/gdm/locale.alias.  By default, the character set for every 
county using the EURO currency is set to ISO8859-15 in order to enable the 
EURO sign. If you don't feel comfortable with this, edit this file according 
to your preferences.

If you are running 5.x and you are running 5.1-RELEASE or earlier, GDM will 
fail to work due to a bug in OpenPAM.  You can download a patch from
http://www.FreeBSD.org/~marcus/pam_get_user.c.diff.  You must also have the
FreeBSD src tree on your system.  Do the following to apply the patch:

# cd /usr
# patch -p < /path/to/pam_get_user.c.diff


Then rebuild and install world.  Note, this bug does _NOT_ affect FreeBSD
4.x.