WindowCurl is a free to use program which allows you to turn any window just like a book page, you just need to press ctrl+Drag the corner of the window which you want to turn and see what is behind it.
As shown in the image above, it must be very clear now for you how to curl any opened window, you just need to press ctrl and drag the application around the left top corner of the screen.
The actual windows will curl like this as shown in the image below. This program has a small system tray icon which keeps on showing in the tray when the application is running.
Note: As happened to me this small program might not work in vista.