1) in example.css, there's a fixed height commented out:

=======
/* If you don't want the tab size changing whenever a tab is changed
you can set a fixed height */
/* height:200px; */
=======

uncomment the height and make it:
height:100%;

2) Close out the table at the end of your html. And you can put another row/cell in there at the bottom to "force" your box up top (hoaky but it looks better). So the end of your html will look something like:

....
	<div class="tabbertab">
          <h2>Spare Tab</h2>
          <p>Content for another Tab</p>
     </div>

</div>

</td>
</tr>
<tr height="100%"><td height="200"> </td></tr>
</table>

</body>
</html>

Give that a shot.