Display to guests?

[Impreza04]

Ive been trying to add a message to my archive pages to encourge guests to register. However, no matter what I try the message either displays to everyone or not at all.

Its being inserted as a plug in, in archive_postheader.

PHP Code:

echo "<div class=\"post\">$vbphrase[archive_guest]</div><br/>"; 

But no matter what i wrap this in, it wont display to just guests.

Any help?
Cheers