I've just been fiddling with my test installation and managed to get Moodle to authenticate against an NT password using UserServer found here http://clauer.free.fr/php/userserver.zip. I thought someone else might be able to use what I've found.
A few modifications to the login index.php were needed. But nothing too drastic. As far as Moodle is concerned, everyone's password is the same, currently 'password' but could be anything, and this is hard coded.
if (CheckPassword($username, $password)) {
$user = authenticate_user_login($frm->username, 'password');
.... other moodle code
}
else {
$errormsg = get_string("invalidlogin");
}
CheckPassword is a php function supplied with userserver which returns 1 if the username/password is valid.
Obviously accounts need to be created with user names matching the NT ones, but I will be creating the accounts anyway, so this isn't a problem for us.