PHP Code:
<?php global $post;
$rand_posts = get_posts('numberposts=6&orderby=rand');
foreach( $rand_posts as $post ) : ?>
<a href="<?php the_permalink($page->ID) ?>" title="<?php the_title(); ?>">
<?php echo get_the_post_thumbnail($post->ID, 'thumbnail'); ?></a>
<?php endforeach; ?>
Another snippet that should help.