The old one was a PHPBB2 forum that was separate from the main site, this one is custom built into the new site.
The main difference with the new forums is that I have ditched the categories, no one ever posted in the right category anyway so there was no real need for them.
Now when you make a new topic or reply to a topic it will jump up to the top of the page. The forum home page will show 20 topics per page.