Y'know, I did something similar to my stepdad when I was living with my parents. Using Gimp, I took a screenshot of the desktop, set the image to be the desktop. Then move all the icons on the desktop to a new position, take another screenshot and set it again as the desktop background. (This works best if you set it so your icons do no Align To Grid.) Rinse and repeat like 50 times. Each time, a new set of pictures of icons that don't work will be on the desktop, along with a little inert taskbar on the bottom. (Initially, covered by the real taskbar). When all finished, move all the real icons off the desktop and minimize the size of the taskbar and shift it to one of the sides of the screen.

The result is that it looks like there are a huge number of icons on the desktop and yet none of them work. Also, there will be a little taskbar at the bottom that does nothing. Took them forever to figure that one out =)