noo...man you`re doing it all wrong...freebsd uses ports & packages system that makes isntalling new apps or upgradeing really easy...i recommend you to read freebsd handbook, you can find it on
www.freebsd.org, or in your /usr/share/doc dir. Whole process about installing new app in freebsd is eg. pkg_add -r gimp or from ports cd /usr/ports/graphics/gimp1
; make install clean
it will fetch it from net and install it.
ports system is great :o)
i cannot help you with gdm part, cause i`m not using it, you can use gnome without it...