Ordnance Survey wallpaper as desktop
This works for 1280x1024, if you have a different resolution go to http://www.ordnancesurvey.co.uk/oswebsite/freefun/wallpaper/ and pick the closest, and put in the file url. Then just set your wallpaper to the file from you dropbox directory. Having tested it doesn't overwrite the file, so the wallpaper doesn't automatically update.
Applet ID 44676p