Ok,
I got it working on Snow Leopard. Here is what I did.
1. Install MacPorts... this will make it a whole lot easier.
http://www.macports.org
2. Once you get ports installed use macports to install the gd lib stuff:
sudo port install gd2
This will also install perl 5.8.9... perl 5.10 comes with Snow Leopard. Not sure it any mac stuff requires that... but you can always go back, macports puts stuff in a separate location.
I also installed the following macports:
p5-gd
p5-palm
p5-timedate
p5-getopt-mixed
p5-image-size
p5-xml-parser-lite-tree
p5-encode
Then, I use CPAN to install the following... there didn't seem to be any macports for them:
HTML::TreeBuilder
Image::BMP
After that mobi2mobi ran... well it gave me the command line options. I didn't actually try it. But, it doesn't seem to run unless all the dependencies are there.
I expect that if you just use MacPorts to install the gd2 stuff... which install all those dependencies like zlib, libtool, libjpeg, libpng, freetype, etc... then you can just use CPAN for the rest.
Good luck to you.
BOb