How to re-create the Show desktop icon on the Quick Launch toolbar

To re-create the Show desktop icon yourself, follow these steps:

1. Click Start, click Run, type notepad in the Open box, and then click OK.
2. Carefully copy and then paste the following text into the Notepad window:

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

3. On the File menu, click Save As, and then save the file to your desktop as "Show desktop.scf". The Show desktop icon is created on your desktop.
4. Click and then drag the Show desktop icon to your Quick Launch toolbar.

The Quick Launch toolbar uses the files in the following folder:

%userprofile%\Application Data\Microsoft\Internet Explorer\Quick Launch

Alternative method:

1. Click Start, Run and type the following command:
2. regsvr32 /n /i:U shell32.dll

The Show Desktop icon file should be available now

More can be read here
http://support.microsoft.com/kb/190355