Converting Joomla/Joomlaboard to PunBB

I'm looking at converting a Joomla site to PunBB and have a few questions..
The site is Joomla based, with a JoomlaBoard forum (derivative of SimpleBoard?).

--Has anyone got experience of converting JoomlaBoard to PunBB?
--Does the current converter work?

--Does Joomla (not JoomlaBoard) have its own user accounts?
--Can they be converted into PunBB user accounts easily?

All advice appreciated.

Thanks

--Alan