He's using the DOM to change between display: block and display: none.
Code:
<ul>
<li class="current"><a class="current" href="#">Whitstable Yacht Club</a></li>
<li><a href="#" onmousedown="document.getElementById('StatsHeader').style.display ='block', document.getElementById('StatsBox').style.display ='block', document.getElementById('ImageHeader').style.display ='none', document.getElementById('ImageBox').style.display ='none'">Stats</a></li>
</ul>
You can do it using pure css like this guy's done with his right hand column.
http://www.1976design.com/blog/
Play around with his stylesheet to see how it works.
__________________That's fuckin' ingenious, if I understand it correctly. It's a Swiss fuckin' watch.