I'm going to be starting up some forums for my web-based game (written in PHP) soon, and I know I want to use phpBB, but I'm not sure whether to use phpBB 2 or phpBB 3. I know that phpBB 3 is currently less stable, but I am tempted to use it for its added functionality etc.
I'm wondering if phpBB 2 databases are compatible with phpBB 3 databases. I.e., could I start out with phpBB 2 and have the community build up, then once a stable release of phpBB 3 is released, upload all the phpBB 3 files over that and expect everything to be fine? I doubt if all of the database structures would remain the same, but particularly I'm focused on the users table (read next paragraph to see why/how) and the forums and posts (so that old discussions will remain on the database).
Why I need "users" table compatibility: I want to have my game accounts and my forum accounts link up (so you register on the game, and it will insert a new user into the phpBB users table with the same username/password/email address).. this way, users only have to register once, and I can have the forums retrieve the user's data from the game (to display character level, print out the character's avatar as the forum avatar, etc.).
So I'm mostly considering starting with phpBB 3 if it's difficult to upgrade from phpBB 2 to phpBB 3, and then just living with that and upgrading from the phpbb3 unstable release to the phpbb3 stable release when one is released.
What do you think? Is upgrading from phpbb2 to phpbb3 easy, or should I just start with phpbb3?