if ($context['user']['is_logged'])
echo '
<td align="center" valign="top"><img src="' . $settings['images_url'] . '/menu_devider.gif" width="31" height="28" alt="" /></td>
<td class="mainNav"><a href="', $scripturl, '?action=shop">Shop</a></td>';
Just paste that into your index.template.php in the section with all the other buttons in it.