This might help you on that.
1. Right click your desktop, go to View, and click "Show Desktop Icons" and "Show Desktop Gadgets"
2. Open a window, resize it till it's covering the full screen (but not maximized, don't think that would work, though I can't check)
3. Hover over the Show Desktop button.
4. There's a key on your keyboard that says "Prnt Scrn" (that might not be the same for yours, but it's near the top righthand side of your keyboard). Hit it.
5. Go to Paint, click Paste, and you should have the image with the Aero Peek effect.