Good news! It appears this plugin has been picked back up. This is great as it is really the only thing out there that brings phpbb and wordpress together. I have installed it and am using it on FyxtRPG.com and it is working well. I am not using the more advanced features, just the shared login. But so far so good!
After some investigation it appears the plugin author for this has not been active in either the WordPress or phpBB communities since March 11, 2013. It does not appear this is supported anymore. It is probably a bad idea to use it now.
If you are looking for a way to integrate phpBB with WordPress it seems that WP-United : phpBB WordPress Integration is the way to go. I have only started working with it but it seems to work quite well to bring phpBB into WordPress. It is great to be able to have such a robust forum inside of WordPress. I will post more when I have a better feeling for it.
For now I am going to post a few of the support files that are needed for it since their website seems to be temporarily down.
You will need to have AutoMOD installed in your phpBB board. That can be found here: https://www.phpbb.com/mods/automod/
Then you will need the mod by WP-United. This can be downloaded: wp-united-release-phpbb.zip
Just upload that file in AutoMOD in the ACP of phpBB and you should then be able to connect and manage your users.