I installed a handy wee mod recently called Sitemap Generator on a couple of my forums, obviously it does exactly what it says on the tin, it also pings google to give it a kick to come and check out the changes.
Having only installed it just over a week ago I didn't think I would notice much of a difference, but already I have noted more google traffic finding its way into the forums.
It is definitely worth checking out, and of course it totally free!
http://www.phpbb.com/community/viewt...?f=70&t=600289