I built this site a while ago, and the client did something to break it, but I'm not sure what.

This is the error: '[function.include]: failed to open stream: no suitable wrapper could be found in /homepages/15/d206436658/htdocs/wsb4535514701/zenphoto/themes/default/album.php on line 1'

What would cause that?

Take a look at that line in the actual theme on installed on the site. The error is saying that some kind of include failed, but the standard "default" theme has no such include on line 1 of album.php. Perhaps that file has been compromised

I put an include in the theme when I built it, and the include is indeed there.

Here's an example of a broken page: http://www.bmengini.com/zenphoto/index.php?album=Dance/

And yet the include really is there: http://www.bmengini.com/includes/top.php

When I visit that site I get the following error:
Warning: include() [function.include]: URL file-access is disabled in the server configuration in /homepages/15/d206436658/htdocs/wsb4535514701/zenphoto/themes/default/album.php on line 60

This is an indication that the filename you have used in the include is a WEB based URL, not a filesytem one. Probably what has happened is that the site providers have tightened up their security a bit and are now disallowing URL file access (see the message) whereas before they did allow it.

So essentially, I have to target it using a filesystem path, correct?

Is there any way to determine how many levels I have to go up, or do I just punch in ../ until I get it?

Yes, you probably have to try that. I guess ../includes/(...) might work if Zenphoto is within /zenphoto.

That did it. Thank you both! I appreciate it!