Zufällige Posts aus einer Kategorie anzeigen?

<?php $display_categories = array('8','4','5','3','9','6','7');
foreach ($display_categories as $category) { ?>
<div class="column span-4 last">
    <div class="five_posts">
<?php query_posts("showposts=1&cat=$category");
        $wp_query->is_category = false;
        $wp_query->is_archive = false;
        $wp_query->is_home = true;
         ?>
        <h6 class="category_head"><a href="<?php echo get_category_link($category);?>"><?php single_cat_title(); ?></a></h6> 
<?php while (have_posts()) : the_post(); ?>
        <?php
        $values = get_post_custom_values("thumbnail");
        if (isset($values[0])) {
        ?>
    <a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><img class="photo_align_left" src="<?php $key="thumbnail"; echo get_post_meta($post->ID, $key, true); ?>" alt="<?php the_title(); ?>"  /></a>
    <?php } ?>
<h6><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>" class="title"><?php the_title(); ?></a></h6> 
        <div class="excerpt_small">
<?php the_excerpt(); ?>
        </div>
<?php endwhile; ?>
</div>
</div>
<?php } ?>