[kh99]

You could look at admincp/user.php, search for "Start do update". (It's the code for adding a user from the ACP). I think this line:

$userdata =& datamanager_init('User', $vbulletin, ERRTYPE_CP);

creates an instance of that class. But if you did your own db writes because you didn't want to use a lot of the vbulletin code then you probably wouldn't want to use that class.