GD font handling

Hi all,

I'm a relatively clueless user of GD in a PHP environment. I would
like to have more information about GD's font handling. I have a
custom unicode TTF font, made by a colleague using Fontlab (on a
Macintosh) on top of a normal Times TTF unicode font.

This font does not work when I try to render any portion of text into
an image on the fly in GD/PHP. My code is not the problem - with all
my "normal" unicode fonts, it works. Just not with this custom unicode
font. I'm wondering what I have to tell my colleague in order to make
it work. What sorts of TTF format or specification must be used with
GD?

Thanks in advance!
Jeff S.