[James Birkett]

The only step I can give you on this is in register.php lines 346 -> 357.

That piece of code:

PHP Code:

if ($vbulletin->options['verifyemail'])
    {
        $newusergroupid = 3;
    }
    else if ($vbulletin->options['moderatenewmembers'] OR $vbulletin->GPC['coppauser'])
    {
        $newusergroupid = 4;
    }
    else
    {
        $newusergroupid = 2;
    } 


assigns the user to the default usergroup.

My guess would be that you would want to manipulate that code (or use one of the plugin hooks) to change $newusergroupid to the usergroup ID selected by the user.