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

  1. Click Start, click Run, type notepadin the Openbox, 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 Filemenu, click Save As, and then save the file to your desktop as “Show desktop.scf”. The Show desktopicon is created on your desktop.
  4. Click and then drag the Show desktopicon to your Quick Launch toolbar.

Content Source = http://support.microsoft.com/kb/190355 (link includes Microsoft “Fix It” Solution)