Take a screen shot of his desktop and use it as the backdrop.
Then select all the real desktop icons and hide them off screen.

Instant fun as he double clicks on the picture trying to open "My Computer"... =)

Two links with more of the same...
http://www.littlewhitedog.com/reviews_other_00015.asp and
http://www.littlewhitedog.com/reviews_other_00019.asp.

For educational use only though... =)

Jazz
(List 112, Mk2 12 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)