WP-United is the No. 1 Choice if you want to integrate WordPress and phpBB

I tested this plugin since there were beta-releases. It nearly worked perfectly at that time. But now, on my live pages with the released versions, everything runs fine for me.
If there were any questions I got support at the plugin’s forum, could help translate and give some thoughts on what could (be) change(d) to make this plugin even better.
To sum it up: If you are using WordPress and looking to integrate a free forum software – give phpBB a try and use this plugin. It’s easy to install by using AutoMod in phpBB and Plugin-Install in WordPress. 2 more clicks and it’s done.