Previous post link to arbitrary URL

Prior to installing WordPress on my website, I created several ‘posts’ that I would like my “previous post” link to, following these rules:

1. Look for WordPress created posts
2. If no WordPress-created post exists, link to a specific URL

How can that be accomplished?

The several things I have tried have not worked and i am having a difficult time finding info online. Here is my code:

<?php define('WP_USE_THEMES', false); get_header(); ?>
<link href="style.css" rel="stylesheet" type="text/css" />


<table id="Table_03" width="855" border="0" cellpadding="0" cellspacing="0">
        <tr style="height:251px">
            <td width="162" valign="top" align="right"><br><br><p>
            <a href="../../../../about.php"><span class="text6">about us  </span><span class="text4">/</span><br>
            </a><p>
            <a href="../../../../culture.php"><span class="text6">our culture  </span><span class="text4">/</span><br>
            </a><p>
            <a href="../../../../partners.php"><span class="text6">partner profiles  </span><span class="text4">/</span><br>
            </a><p>
            <a href="../../../../CEDA.php"><span class="text6">CEDA  </span><span class="text4">/</span><br>
            </a><p>
            <a href="../../../../news.php"><span class="text4">news  </span><span class="text4">/</span><br>
            </a><p>
            </td>
            <td width="59" valign="bottom" align="left"></td>

            <td width="532" height="330" valign="top" align="justify"><br><br><p>
            <span class="text4">news  /</span><br>
                <?php if (have_posts()) : ?>  
                <?php while (have_posts()) : the_post(); ?>  
                    <div class="post" id="post-<!--?php the_ID(); ?-->">  
                    <div class="entry; text5"><?php single_post_title(); ?></div><p>          
                    <div class="entry; text5"><?php the_content(); ?></div>  
                    </div>  
                <?php endwhile; ?>
            <td width="102" valign="bottom" align="left"></td>
        </tr>
</table>

<table id="Table_07" width="855" border="0" cellpadding="0" cellspacing="0">
        <tr>
            <td width="221" height="20"></td>
            <td width="532">  
                <span class="class6" style="float : left; text-align : left;" align="left">
                    <?php previous_post_link('%link', 'previous /', TRUE ); ?></span> 
                <span class="class6"  style="float : right; text-align : right;" align="right">
                    <?php next_post_link('%link', '/ next', TRUE); ?></span>
                    <?php endif; ?> 
            </td>

            <td width="102"></td>
        </tr>
</table>
<?php get_footer(); ?>