While waiting for the 1.0.3 release (hopefully before I go to bed), I decided to stop working on my hack (which might change depending on how 1.0.3 is) and finish up my Wiki article on how to make a theme for ZenPhoto.
I tried to make it as easy as possible (while still allowing me to be as lazy as possible =P ).
Anyways, if you're interested, you can view it HERE. (NOTE: This article is very outdated)
EDIT (more theme documentation):
New Theming Tutorial: http://www.zenphoto.org/2008/05/theming-tutorial/
Functions guide (official version): http://www.zenphoto.org/documentation-official/index.html
Functions guide (svn/nightly): http://www.zenphoto.org/documentation/index.html
Forum post with function help: http://www.zenphoto.org/support/topic.php?id=132&replies=13
Upgrading themes to 1.1: http://mitcho.com/blog/2007/11/04/updating-your-zenphoto-theme-for-zenphoto-11/