[Martin64]

Here's what I would do.

1. Create a new template, name it "galleryerror" and put whatever error message you wish to display in it, ie:

Sorry, if you wish to view the Gallery you must be a registered member

2. Open gallery.php.

FIND:

if ($bbuserinfo[userid]==0) {

  show_nopermission();

}

REPLACE WITH:

// unregistered error message
        if ($bbuserinfo[userid]==0) {
          eval("standarderror(\"".gettemplate("galleryerror")."\");");
        }

Not tested but should work. I hope it's what you're looking for.