to disable the preview desktop with aero peek feature on windows 7 all you have to do is right click on your taskbar and select properties, in the taskbar tab, at the bottom you will see the "Preview desktop with Aero Peek" section

Temporarily view the desktop when you move your mouse to the show desktop button at the and of the taskbar.
[] Use Aero Peek to preview the desktop

make the changes and click OK

NOTE: as you can see mine is shaded, this is because the them i am currently using does not suppor Aero-peek
done

If you see the Window Color and Appearance dialog box instead of the Window Color and Appearance window, you might not be using an Aero theme or your computer might not meet the minimum hardware requirements for running Aero. To learn more about Aero, see What is the Aero desktop experience?