This plugin bridges your Vbulletin users over to your Wordpress script.
You can map your Vbulletin Users to Wordpress Userss and those users will then be seen as registered Wordpress users.
For example, user “Bob” registers at your forum and logs in. Bob then clicks on your Wordpress page. Bob is instantly added to the Wordpress user base with the permissions you set for his user group. In otherwords, if a user comes over belonging to the “Register User” group, you can select that he is placed in the Wordpress “Subscriber” user group.
If you change a users user group, it will automatically change in Wordpress.