1- From the explorer, open the following folder : C:\Documents and Settings\[Your Account Name]\Application Data\Microsoft\Internet Explorer\Quick Launch

2- Create a new text file and insert the following content :

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

3- Save and rename the file : ShowDesktop.scf

The icon will appear in the quick launch bar !