Thank you for your answer.
I'm using only 1.5, so I think there is no practical workaround, bur thanks a lot.

Also a pre-sale question. On my site, there is a forum, where everyone can register. The joomla content for the registered users is only for members of a fan-club. So my question is: Can I only syncronize some selected users from phpbb to joomla or is it an automatism to open the registered content ...