Anonymous user creates node -> how to get the new member name of this user to his node?

I fight with the following: when an anonymous user creates a node and saves it a product is added to the cart. When this user goes to checkout, he can choose username and password on his own or a new account is created. My problem: when he finishes payments I found the following way to change some things on the originally created node of this customer using conditional actions and the following code:

if (isset($order)) {
  foreach ($order->products as $product) {
    if (isset($product->data['node_checkout_nid'])) {
      $node = node_load($product->data['node_checkout_nid']);
      $node->field_status['0']['value'] = 1;
      $node->field_orderid['0']['value'] = $order->order_id;
      node_save($node);
    }
  }
}

Found here: http://drupaleasy.com/blogs/ultimike/2009/03/event-registration-ubercart

Here I would like to add adtionally the name of the new user account to the node/ the user ID of the customer as the authors ID to the node. Has anyone an idea, how I can do this?