If you mistakenly deleted the icon for the Desktop on the Quicklaunch toolbar Go to C:\Documents and Settings\user_name\Application Data\Microsoft\Internet Explorer\Quick Launch
(where user_name is replaced by your login name)

Create a Text file called ShowDesktop.SCF with the following contents:

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