PC Wallpaper Instructions: Right-click on the image and choose "Set As Wallpaper"

MAC (OS 9.x) Wallpaper Instructions: Drag the image on to your desktop. Go to Apple menu > Control Panel and select "Appearance". Select "Place picture" and locate the appropriate wallpaper. Click "Set Desktop".

MAC (OS X) Wallpaper Instructions: Drag the image on to your desktop. Go to Apple menu > System Preferences > Personal section and select "Desktop". On the "Collection" pulldown menu, go to "Choose Folder" and locate the appropriate wallpaper.