Login using vbulletin database

[TheHeartSmasher]

I am trying to build a web app where when the user logs in they login with their vbulletin forum account, but can only login if they are apart of certain groups, then their access from their is different.

I used this tutorial to create my login box.

I also have this installed on my forums which works perfectly with any php applications I build.

The problem I am having is for my login box is have the password encrypted using vbulletin's encryption method "md5(md5(PASSWORD).SALT)" then passed onto the login.php file then coming back to log the user in.