This page is designed to use web standards. You are using a browser that does not properly handle these standards. The website will work properly (it just won't look so hot) so you should consider upgrading. Any modern browser should work fine (Safari, Mozilla, IE, etc.)
Visit the Web Standards Project for more information.
For all those people who I pester to use XHTML. Now an easier way; HTML Tidy! For the Mac users out there, MacTidy which can either be used as a standalone application or (even better) as a BBEdit plugin! And for those using other operating systems you can look at the main page - HTML Tidy