If you follow th directions at the end
Login to your AddonChat Control Panel at
http://www.addonchat.com/login.php. Click the Control Panel Icon next to the account that you wish to integrate with to open the Account Control Panel. Click the Settings tab. Click Site Integration. Click Remote Authentication in the Site Integration submenu. For Authentication URL, enter a direct URL to your chat_auth.php script. I.e.,
http://www.myforums.com/chat_auth.php. Make sure that the "Enable Authentication URL" setting is set to "Yes" and click the Save Here to Changes button. Authentication into your chat room will now be performed from your vBulletin user database.
In order to get the Remote Authentication you have to pay 120.00