adding text...

I'm making my gallery so people have to register and log in to view photos. When someone who is not logged in goes to an album, it shows up as <!-- BBCode Start --><A HREF="http://kclarkson-media.org/ai" TARGET="_blank">this</A><!-- BBCode End -->. I would like to have some text where the images would be (if the person was logged in). Something like "You must register an log in to view this album." or something of the sort. That way, people aren't going crazy wondering why they can't view the album. I tried figuring out how to do this myself, but I wasn't successful. If someone knows how to do this and could tell me what file to edit and where, I'd appreciate it. Thanks!