+1  A: 

a PHP file with a 301 HTTP permenant redirect.

Put the following into index.php in the root directory of guardthe.net

<?php
Header( "HTTP/1.1 301 Moved Permanently" );
Header( "Location: http://guardthe.net/punbb/" );
?>

browser will re-direct with search engine friendliness.

Unless there is no mod_rewrite support on your server, you should avoid this approach as the user must download this web page and have the browser display it before executing a second transaction back to the server. The delay is usually long enough for the user to notice. Go for mod_rewrite if poss.
Cheekysoft
A: 

Your example code is missing but here's one way to do it using mod_rewrite:

RewriteEngine on
RewriteRule ^$ http://guardthe.net/punbb/ [L,R=301]
Jan Krüger
Just a note to clarify:This would need to be in the webroot's .htaccess file, (not within the the punbb directory).
Peter Boughton
A: 

You could write a small redirect script to take care of this simply and quickly.

<?php 
header( 'Location: http://guardthe.net/punbb/' ); 
?>

Enter that as the only content in your index.php in your root directory, and any requests sent to that folder will then redirect the user to the forum.

toluju
+2  A: 

Something like this in .htacces should do it:

    RewriteEngine On
    RewriteRule ^/?$ /punbb/ [R=301,L]

The 301 return code is to mark the move as permanentm making it posible for the browser to update bookmarks.

Mr Shark