[Rik Brown]

Yes, there is a "bridge" named jFusion that lets you register or login once to both vbulletin and Joomla at the same time. We use it with vBulletin 4.2.x and Joomla 2.5.x.

We have it setup so that vBulletin controls the logins since there are better anti-spam protections around for vBulletin. But you can just as well go the other way around and let Joomla control the logins.

I could never get it to retroactively sync 100% our older vBulletin users. But it syncs fine any new users or when an older user who hasn't been on for a while returns. So we haven't lost any users due to that problem (which seems not to happen to other installations, anyway).

-- Rik