The Show Desktop icon in the Quick Launch toolbar isn't a normal shortcut.
If you accidentally delete it,you can't recreate it the way you would a
shortcut to a program. Instead, launch Notepad and type these lines:
[Shell]
Command=2
IconFile=explorer.exe,3
[Taskbar]
Command=ToggleDesktop
Save the file with the name Show Desktop.scf in the folder C:\Documents and
Settings\ username\Application Data\ Microsoft\Internet Explorer\ Quick
Launch, where username is replaced by your actual user account name.