Vista/XP Virtual Desktop Manager

One of Vista's most talked-about new features is the Desktop Window Manager (DWM). A new set of thumbnail API's can be used to access thumbnails of open windows. This virtual desktop program takes advantage of this new API and uses some tricks of its own to provide a powerful virtual desktop manager with a full screen thumbnail based preview. You can have as many desktops as you want and can seamlessly switch between them.

http://www.codeplex.com/vdm

But wait! What if you still are using XP? Don't worry, Vista/XP Virtual Desktops provides support for XP as well, although window previews are not live since XP doesn't have DWM.