vBulletin User Integration
The vBulletin user integration module will add vBulletin users to your Pligg website. It works by adding vBulletin users into the Pligg user database either when the user signs in using their vBulletin credentials or by using a vBulletin cookie to automatically log them in.
Note: You should change all links register page to point to your vBulletin registration page. You should also set your register template to either redirect to your vBulletin page or simply remove the content from that template.