Is it possible to allow users to add tags as well as admins? I would like some of my users to help me organise some of my photos by adding tags but I can't see that this is possible currently without making them admins.

zenphoto does not have the concept of "users". You can, however, create "Administrators" and give them the necessary rights to edit albums. This will give them the ability to add tags. If you have just a few people who you would like to help, Adminsitrators is the way to go.

Thanks for the response. Is there anyway to just let anyone add tags. I shouldn't have used the word user, I meant just anyone viewing the website.

No, those kind of editing functions are restricted to administrators.