we do you need 2 seperate user tables? Wouldnt 1 user table be enough for your site? Instead of syncing the users why not just change Joomla! to use Vbulletins user tables since VB has stronger user fields, registeration options, etc, etc. I have already produced a alpha copy of this bridging process and will release a demo site in the very near future possibily by the end of the week for a demo site

If you would like to see it in action sooner PM me on these boards and ill send you a link to my current forums but i dont want a massive amount of traffic going there so until i get my other site setup the way i want i cant post the link quite yet.
Also what modules do you think would be good for a VB-Joomla site so far i have managed to create the following
- Top Ten Posters
- Hot Topics ( Threads )
- Whos Online
- User Welcome Box w/ PM Stats
- VB Template Intragration into Joomla!
Are there any special features you would like to see added to a bridge? etc etc etc