It is fairly easy to restore the "Show Desktop" button that usually resides in the Quick Launch toolbar, if you have removed it.
Open notepad and paste the following:
[Shell]
Command=2
IconFile=explorer.exe,3
[Taskbar]
Command=ToggleDesktop
Save the file as "Show Desktop.scf" in C:\Documents and Settings\<YOURNAME>\Application Data\Microsoft\Internet Explorer\Quick Launch where YOURNAME is the username of the account that is missing the icon.
