Dynamic Submenu Navigation

I am trying to get a sub menu set up for my site. I need it to be like this on top-level pages

• Overview
• Page One
• Page Two

Sub Pages

• Overview
• Page One

• Sub-Sub Page One
• Sub-sub Page Two

• Page Two

How can I do this? I know I can use this:

<?php
                  if($post->post_parent)
                    $children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0"); else
                    $children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
                      if ($children) { ?>
                        <ul class="submenu">
                          <li><a href="<?php get_permalink($post->post_parent); ?>">Overview</a></li>
                          <?php echo $children; ?>
                        </ul>
                <?php } else { echo '<ul class="submenu"><li>Overview</li>'; }  ?>

Thanks for any help.