You know, I've seen this issue pop up periodically in the forums. I think there might actually be a certain scenario where there is actually a problem - both times I installed ZenPhoto (for myself, and for a friend), I had the same problem. At first, I thought I just did something wrong setting the admin name/password. But the second time after the install he couldn't login with the name/password I gave him, and it didn't work for me either, and I had to manually edit the database to fix it also. In the second case, I hadn't setup the email address yet, so I thought maybe the lack of an email address caused it, but never followed through on looking into it.