yes you have to do it by yourself. most of the tables are pretty much the same, except that the phpbb_post table contains now the text of the message that is in a separate table on phpbb.
when you have the script it would be nice to give it to us.
I just came up with this same question. Looks like there isn't any ready solution, so I'll work with this and I hope to come up with somekind of migration tool or database converter during next couple days. I'll keep you posted.
I keep small hobby related phpBB 2.0.6 forum (~ 5.5K unique visitors per month) and since I work with JBoss and J2EE in general as my real job (Project Manager / Senior J2EE Developer), I want to change thse forums into platform that feel more comfortable to work with.