WordPress.org

1. unzip punbbrecenttopics.zip in your /wp-content/plugins/ directory. (You'll have a new directory, with this plugin in /wp-content/plugins/punbbrecenttopics)
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Configure the plugin, you need to tell wordpress about punbb, this is done in the wordpress menu 'Options' -> 'punBB Recent Topics' The following Settings are required: * The name of your punBB database (e.g punbb) * The name of the table where topics are held (the default is punbb_topics ) * The full url of your forum for links (e.g. http://www.mydomain.com/forum) * The number of topics to show. (If left blank you get 5)
4. Hit 'Update Options"
5. To output the list of topics in a page or post... * create a new page/post, type {punbbrecenttopics} , hit 'Publish' or 'Create new page' To output the list of topics in your theme sidebar... * edit sidebar.php and inside type...

more information: http://varios2.wordpress.com/2008/04/25/punbb-recent-topics-wordpress-pluging/