Click the download link above or Right-click the wallpaper and choose Set as Background or Set as Wallpaper.
Mac OS X:
Drag it onto your desktop, go to System Preferences, go to the Desktop icons, click the Collection drop-down and Choose Folder to find the new wallpaper on your computer.
Mac OS 9:
Drag it onto your desktop, go to Control Panel and choose Appearance, click Set Desktop and choose the new wallpaper that you just downloaded.