Actually the OSX version of GGMud uses the X11 version of GTK, it's available as App bundle.
To be able to run it you need to install the Apple or the Fink X11 server and run it, you can find apple X11 on your panther/tiger install DVDs as X11User.pkg.
NOTICE: If you are able to run GIMP or OpenOffice you already HAVE the X11 server installed.