I recommend using OnePress Community (http://onepresscommunity.com) to accomplish this.
While it won’t do exactly as you are asking (as far as using the wordpress header and footer) it does integrate the navigation and user logins. As far as templates go, you’ll still have to create a phpBB style but it’s really just a matter of copy and pasting CSS after you have done your WP theme…
You should check out OnePress Community It’s a theme that provides full login integration with phpBB. There are also widgets included that will show recents threads, etc.
