See http://windows7center.com/tutorials/how-to-really-pin-the-show-desktop-to-taskbar-in-windows-7/

>>Create file Desktop.scf and copy it into quick launch
>>

>>[Shell]
>>Command=2
>>IconFile=explorer.exe,3
>>[Taskbar]
>>Command=ToggleDesktop
>>

>
>Thanks, this allows me to create the icon. But, on that particular one, when moving it over the taskbar, we cannot pin it. We can only pin regular icons. That one is locked in Windows 7. I don't know why. But, when I move that icon over the taskbar, the only thing I see is the ability to pin that icon on top of existing icon.