Trevor, Michael and others [concerning GTK on MAC],
I don't know anything about this but did some searching as I am
interested in seeing the GTK approach work. I ran across an article
talking up the possibility of developing GTK applications on the MAC
with a link to a tutorial on how to do this on the MAC. Please look at
this and see if it helps at all with what is needed.
The need for GPL Free Apps on Mac OS X:
http://osnews.com/story.php?news_id=10867
reference in article is steps to set up GTK on MAC:
http://gimp-app.sourceforge.net/gimp.app.howto.txt
I hope this helps.
John