PC - Click the resolution that your monitor is currently set to. Once the image is displayed in a browser window, right click on it and select "Set as Wallpaper".

MAC - CNTRL + click on the image to save it to your hard drive. OS9 - Under the Apple menu, open Control Panel/Appearances. Click on the desktop tab, then click "Set Desktop". OSX - Open your Systems Preferences and click on the desktop icon. Drag the image you want as your desktop into the "Current Desktop Picture" thumbnail.