I have found two freeware applications for you that will do the trick. One plain and simple and one with a few more options.
This is also for those of you who desperately miss your MAC taskbar, but have to use XP at work or whatever. Curious? Read on!
Visual Task Tips (What you expect, is what you get)
Visual Task Tips is a straightforward little application that gives you exactly what you’d expect. A Thumbnail Preview. Nothing more, nothing less. Just Download and install.
Visual Task Tips Supports both 32bit and 64bit platforms.
Visual Tooltip (The one for MAC lovers)
You can control where the thumbnails appear as well as how they appear.
With Visual Tooltip you can also replace your Windows Taskbar entirely with a
MAC-Look-A-Like Taskbar similar to the one found i OS X.
We previously covered this program here a couple of years ago and it seems to be running even more smoothly now.