movie.php

<?php
class Movie extends AppModel {
    // ...
    var $hasMany = array(
        'Attachment' => array(
            'className' => 'Media.Attachment',
            'foreignKey' => 'foreign_key',
            'conditions' => array('Attachment.model' => 'Movie'),
            'dependent' => true,
    ));
    // ...
}
?>

movies_controller.php

<?php
class MoviesController extends AppController {
    function edit($id = null) {
        // ...
        // $this->data = array(
        // 'Movie' => array('id' => $id, 'title' => 'Vicky Cristina Barcelona'),
        // 'Attachment' => array(
        //     0 => array('file' => transferable item1, 'model' => 'Movie'),
        //     1 => array('file' => transferable item2, 'model' => 'Movie'),
        // ));
        $this->Movie->saveAll($this->data, array('validate' => 'first'));
        // ...
    }
}
?>