Minimize all windows button in Win-XP

I have two computers running Win-XP and in both the “minimize all windows” or “show desktop” button is gone. Is there any way to get it back?

http://support.microsoft.com/kb/190355

In all modern versions of Windows, with or without the button: Winkey+D or Winkey+M. They have slightly different behavior, the “D” version works better. Sure, having the button back is good, but I don’t even use it anymore.