You should check out www.meebo.com ! It's supercool.
Although the only purpose of it is functioning as a multi-protocol (AIM, ICQ, Yahoo, MSN, Jabber and Google Talk) instant messenger, it looks more like an operating system in a browser window!
If Microsoft would take the same concept into action, they can create a real life Windows demo that would instantly run in the browser window through the latest and coolest web technology called AJAX!
Using this technology they can create live demos of their next operating systems in which demo users can click and explore what they want instead of staring at a screen of slides.
And they can have the real experience as though they already have the OS installed, although it's just a webpage!