1. start>run>type notepad>hit enter>past the following,
[Shell]
Command=2
IconFile=explorer.exe,3
[Taskbar]
Command=ToggleDesktop

2. File>save as>save it as 'Show desktop.scf' (without quotes)

3. You have now recreated the show desktop icon! Now just go back to where you saved it, and drag it over to your quick launch bar.