Howdy! I wrote a forum migration tool for migrating from one tiki site to another. I had designs on expanding that to port from phpBB but as the site has taken off at my place of business, I've been focused on requirements here and been unable to get back to it.
The migration tool can (relatively) easily be used as a framework, or even expanded upon, to provide migration capabilities from other forum software to TikiWiki. The tiki-forum_import.php script should facilitate this. I haven't tried it in 2.0, but I know it works in 1.9 and at one time it worked fine in 1.10 (which is now 2.0).
If you have any questions, feel free to PM me.