If you have firmware version 2.0 or greater and are using a picture as your wallpaper, use the following trick if you have space to the left and right of the screen that the picture does not cover. To get rid of that space, go into the 'Photos' section and view the picture you want to use. Zoom in on it until the picture takes up the entire screen, then press Triangle and choose 'Set as wallpaper'. When you exit back to the main menu, your picture will now take up the entire screen.