Thanks for the link. It seems to me that it is recommanded with some programming knowledge to implement a rss-feed. Or is it already implemented in the download of pun?
It's already implemented, all you have to decide is what to show, and where.
This is what you can get:
active (show most recently active topics) (HTML or RSS)
new (show newest topics) (HTML or RSS)
Just add this where you want it:
<?php include('http://host.com/forums/extern.php?action=new&show=10&fid=5,6,7&type=rss'); ?>
And edit the values to what you want to show.