Visual Task Tips is a lightweight shell enhancement utility. It provides thumbnail preview image for each task in the Windows Taskbar, like in the upcoming Microsoft Windows Vista.
NOTE: Windows XP required to run Visual Task Tips.
Visual Task Tips is a quite simple utility. Just download and install it.
By using Visual Task Tips you will significantly increase your workflow productivity.
Yes, it's absolutely free for non-commercial use.
http://www.visualtasktips.com/