Click on the page you want to put the image on or right click, select "add image," then highlight the grey square. You can then import any 240x320 image from the properties window. (The import button is the little one with the down arrow.)

Take a picture or retrieve an image from the web and size it DOWN with Photo Shop or equivalent. You can't size up to 240x320 because the image becomes grainy. Microsoft Paint will work but you have to play around with it.

As a general rule though, you don't want to clutter up the background too much because it makes the buttons difficult to read. Do yourself a favor and save busy backgrounds for "Please wait" type pages, for pages with only one or two buttons, or pages for devices with no control at all, like a page you would go to while a Wii is in use.

Enjoy.