As has been stated many many times. phpBB3 is still in beta. It is not suitable for a live environment.
I don't believe the converters have been written yet, as phpBB3 isn't finished, so writing convertors for it would be useless as the code changes daily.
If there is a converter to phpbb2 then you could convert to phpbb2 and then, when RC1 is out, convert to phpbb3. This will almost certainly be quicker than waiting for a converter to phpbb3 to be writtem.
David Remember: You only know what you know and - you don't know what you don't know!
I now no longer support any of my extensions but they will start to become available here