moving people to usergroups automatically

[wtrk]

im using vb 3.-latest and i have a question about moving users to a usergroup based on profile filed answers. in previous version of vbulletin i swear this worked as a plugin with a hook of register_activate_process:

// Get the value for field 
        $user = $db->query_first(" 
            SELECT field7 
            FROM " . TABLE_PREFIX . "userfield 
            WHERE userid = " . $vbulletin->userinfo['userid'] . " 
        "); 

// change user groups

        if ($user['field7'] == 'yes') 
        { 
            $userdata->set('usergroupid', 23); 
        } 
if ($user['field7'] == 'no') 
        { 
            $userdata->set('usergroupid', 24); 

        }

can somebody help me get this to work?