Mostrar imagen grande al hacer click en miniatura

[metacortex]

Prueba así CorpseOfSteel:

Código PHP:

<?php query_posts('cat=1'); ?>
<?php if ( have_posts() ) while ( have_posts() ) : the_post(); ?>   
<?php
$args = array(
    'post_type' => 'attachment',
    'post_mime_type' => 'image',
    'numberposts' => 1,
    'order' => 'menu_item',
    'post_parent' => get_the_ID()
);
$attachments = get_posts($args);
if ($attachments) {
    foreach ($attachments as $attachment) {
        $mini = wp_get_attachment_image_src( $attachment->ID, 'thumbnail' ); 
        $grande = wp_get_attachment_image_src( $attachment->ID, 'full' ); 
        $miniatura= '<img src="'.$mini[0].'" width="'.$mini[1].'" height="'.$mini[2].'" alt="'.get_the_title().'" title="'.get_the_title().'" />' ."\n";
    }
}
?>
<a href="<?php echo $grande[0] ?>"><?php echo $miniatura ?></a>
<?php endwhile; endif; ?>