Silverstripe-vbulletin is a project mainly written in ..., it's free.
vBulletin integration for SilverStripe CMS
This is a SilverStripe module for authenticating against a vBulletin user directory.
If you have set a vBulletin table prefix, define it by putting this line in your _config.php
VBulletinAuthExtension::set_table_prefix('vb');