Well, it works for me, as developers always say! The video is in the top left of the central part of the screen. You can either click on the video box to start it (takes a few seconds to get started on my home connection) or move your mouse over it to see the player controls. The corresponding slides for the talk are displayed in the lower half of the main window.
It works fine for me in Firefox 3.5 and in Chrome (both on a Vista PC but that shouldn't make any difference), so unless you're missing some kind of plugin (Flash maybe?) it ought to work for you too. There are lots of other interesting videos etc on the InfoQ site, so maybe try another one of those to see if it's a problem with this one specifically or if it's a general problem.