Windows (95, 98, ME, 2000, XP)
To change your desktop wallpaper in Windows, simply right-click on the desktop, and choose Properties. On the Desktop (or Background) tab, make your selection and preview it in the little monitor. You can choose whether your selection looks better centered, tiled, or stretched by selecting one of those choices in the box labeled Position (or Display).
To change the wallpaper of your Mac OS X desktop follow these instructions.
1. Click on the Desktop to make the Finder active.
2. Select Preferences under the Finder menu.
3. Change the wallpaper using the Select Picture button.