Leaving Joomla for WordPress MU

Hello,

I was wondering, we’ve currently have a Joomla 1.5 installation and it works like a charm. We also got a blog system using the Joomla user table. The blog system isn’t very great unfortuantly. So, now I’m about to migrate the blog part to WordPress MU. The only problem is the users and how to migrate them to WordPress. I’ve tried to search but haven’t found anything related to my problem. So, is it possible to convert the users without having them to reset their password?

Best regards,

Robert