In order to install this image, if you use OS8, all you have to do is open your Desktop Pictures control panel, click on the "select picture" button, and then go and find the picture via the Open dialog window. Once found, click on "set desktop". That's it.
For earlier systems, I recommend installing the D残or desktop picture extension, by Fran腔is Pottier, available at:
That'll take care of showing and refreshing any background image, and has the advantage of being able to display gif images too, unlike Desktop Pictures.