Does somebody still have the zenphoto theme demo download posted in this thread:

http://www.zenphoto.org/support/topic.php?id=1212#post-7529

I'd appreciate it if the author or somebody would re-post it.

How about contacting the author? I doubt that it will work without issues with today's Zenphoto actually, it seems it needs some core hacking (but just quickly looked at it). Why do you need that?

I did contact the author, so far no response.
I need it because it seems to implement a user theme selector.

I need the theme selector to allow users to select and set their own favorite theme from the set of available themes and also to allow me to more easily test various themes without having to change all the time the settings in the back end.

To test themes, the easiest would be to use your browser's tabs, one with the admin theme page and one with the site. Besides that I can't help, sorry. Maybe someone else still has that.