Occasionally I end working on PC that is missing the show desktop icon. I always end up looking for how to recreate it on Google.
In Windows XP, go the run command then type the following command:
regsvr32 /n /i:u shell32.dll
Then press enter. A dialog will let you know it was successful.
The show desktop won’t be there until you reboot or type the following command:
%appdata%\microsoft\internet explorer\quick launch
This will open a folder. Then you can drag the show desktop icon to your quick launch bar (it will create a short cut in the folder that just opened up).
In Vista, go to howtogeek.com and download the file labeled “ShowDesktop.zip”. Open that file and drag the file it contains to the quick launch bar.