Slideshow with metabox, custom field and query_posts

functions.php

<?php
// Add metabox
function dfw_slideshow_metabox() {
    add_meta_box(
        'dfw-metabox',
        'Slideshow',
        'dfw_slideshow_metabox_content',
        'post',
        'side'
    );
}
add_action('admin_init', 'dfw_slideshow_metabox');

// Add contant for metabox
function dfw_slideshow_metabox_content() {
    global $post;
    wp_nonce_field(__FILE__, 'slideshow_metabox_nonce');
?>

<div id="dfw-ahhc-side-wrap">
    <label for="dfw_slideshow" style="margin-right:5px;"><?php _e('Exibir post no slideshow:'); ?></label>
    <input type="checkbox" id="dfw_slideshow" name="dfw_slideshow" value="1" <?php checked(get_post_meta($post->ID, 'dfw_slideshow', true), 1); ?> />
</div>
    <?php
}

// Save metabox
function dfw_slideshow_save_metabox($post_id) {

    if (isset($_POST['slideshow_metabox_nonce']) && !wp_verify_nonce($_POST['slideshow_metabox_nonce'], __FILE__))
        return;

    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE)
        return $post_id;

    if (!current_user_can('edit_post', $post_id))
        return $post_id;

    if (get_post_type($post_id) == 'post' && $_POST) {
        // Save custom fields
        $value_new = esc_attr($_POST['dfw_slideshow']);
        update_post_meta($post_id, 'dfw_slideshow', $value_new);
    }

    return $post_id;
}
add_action('save_post', 'dfw_slideshow_save_metabox');

?>

index.php

<?php
    $slides = 5;
    query_posts( 'meta_key=dfw_slideshow&meta_value=1&posts_per_page=' . $slides . '&ignore_sticky_posts=1' );
    if ( have_posts() ):
?>
    <div id="slideshow">
        <?php while ( have_posts() ): the_post(); ?>
            <!-- Conteúdo do seu slideshow -->
        <?php endwhile; ?>
    </div>
<?php
    endif;
    wp_reset_query();
?>