To open the folder that those icons are in, carefully right click just to the left or right of the icons down there (it can be kind of hard to hit the right spot). A menu should pop up. Click either open or explore (it's open in Windows 2000, but it may be different in 98, ME, or NT). This should open up a folder called Quick Launch. Now, create a new text file. Put the following inside it:
[Shell]
Command=2
IconFile=explorer.exe,3
[Taskbar]
Command=ToggleDesktop
Save this file in the Quick Launch folder as "Show Desktop.scf" (don't put in the quotes, I just put these in so it's easy to see). Now, your icon should be back. By the way, you can also use Windows-D to do the same thing if you have a fairly new keyboard.