Now this is a feature that should have been added to Windows XP. It matches and reflects the Windows XP visual style. Its really neat because instead of just showing the title and icon of an application, it also shows a screenshot of the applications window. For instance, this is especially useful when switching between instances of Internet Explorer, since you can easily have 5 or more instances running at a time. Well, at least I do pretty frequently. This isn’t something I just discovered, I’ve actually been using it since it was released.

http://www.microsoft.com/windowsxp/downloads/powertoys/xppowertoys.mspx