Visual Tooltip displays thumbnails of a program window when you mouseover its tab on the Windows taskbar. You'll find a number of options, including one to create a separate dock for the thumbnails and optional shortcuts, but this free utility is mostly eye candy.
The download doesn't require installation; just extract the files and double-click the program. The tool then runs from the system tray and pops-up a miniature preview of each program window's contents, along with the full window title, when you move your mouse over each program's button in the taskbar.
The pop-up fades when you move your mouse away, or you can click a thumbtack icon next ot the title to make it stick around. You can also right-click the pop-up to add the thumbnail to a separate dock.
That dock can take over some of the taskbar functions, such as displaying a thumbnail for each running program, as well as the system tray icons. You can add custom shortcuts as well. But you'll quickly miss the Windows Start menu if you try to hide the regular taskbar in favor of using the Visual Tooltip's dock. And if you don't hide the regular taskbar, you'll find that the dock gets in the way of viewing maximized windows.
Visual Tooltip's visual cues look nice, and may help with selecting the right window if you have many different programs open. But if you're after a more full-featured dock program, take a look at the also-free ObjectDock.