I have been attempting this with a site of mine and have had 0 luck. I always get the WSOD and I get logged out of Drupal. As far as I am aware, the drupal/phpBB3 forum integration bridge is a dead project. The release date of the beta was the 11th of July, and there has only been floods of issue posts.
If you have any luck at all, please let me know. I'm setting this thread to notify me when a reply is posted so I keep up with the progress. Mean while, I will start digging through the code to see if I can figure it out.