I just loaded phpBB on one of my sites just to test it out. WOW! I couldn't believe how fast I built a forum just like the one I'm using here at Hostony. It's customizable to quickly add your logo and text. If you haven't seen it, you need to.

I have been playing around with modifying my wifes BB. It is my favorite new hobby, I have a link to share with you that you may find interesting http://www.phpbbhacks.com/
alot of templates (they are easy to add)
also some good code prehacks, for example I am adding sub-catagories now based on code I found there.
Being a "Php" guy you will prolly get even more out of it than I did