OK here it is:
Tested on 1.1.3 and 1.1.4
Demo location: http://www.eDevBoards.com (only if you haven't registered -- otherwise it wont show up )


Setup Instructions:

• Open up the forum control panel and add a template called "guestmsg". In it type the message you want displayed to unregistered users, along with any formatting. I have used the <smallfont> tags to make it fit better on the page.
  
• Open global.php into your favorite text editor and find the following line:
  eval("\$fivelinks = \"".gettemplate("fivelinks")."\";");
  
• Above it, insert the following code:
  
  Code:

  if ($bbuserid == "0") {
  	eval("\$guestmsg = \"".gettemplate("guestmsg")."\";");
  }

• Go into your forum control panel again, and find the place you want the guest message to show up. I have mine at the bottom of the fivelinks template. Type "$guestmsg" in the right place.

Not much of a hack, but anyway