Put content in posts_nav_link()

How is this done?

It’s going to be a photoblog (so lots of people will want to see how this is done)

Simply –
One entry per page – Content is a large image
click on the content, and you are taken to the previous entry.

this is what I have right now, and it’s not working. It takes you to the same entry (and I want to go to one BEFORE this entry.

<?php get_header(); ?>

<?php if (have_posts()) : while (have_posts()) : the_post(); ?>

     <div id="content">

	       <div class="entry">
	            <div class="box-contents">

<a href="<?php echo get_permalink($previous_post->ID); ?>"><?php the_content(); ?></a>

	                 <div class="pie">

<span class="comments">
<?php comments_popup_link('Be the first to comment on this picture', ' (1) Comment', ' (%) Comments'); ?>
</span>
                         </div>
	            </div>
	       </div>
<?php endwhile; ?>
<?php endif; ?>
     </div>

<?php get_footer(); ?>

Anyone have an elegant, simple solution