1. Go to http://www.artchive.com/
2. Click on the ArtArchive/Mona Lisa icon
3. A window with a column of artists is displayed
4. Select an artist from the list
5. A bio of the artist is displayed, select "View Image List" on that page
6. Select one of the images from the image list.
7. Right-click in the image and select "Set as desktop background" -- this sets the picture as your desktop.
Enjoy,
Joanna