Wide Wallpaper for 16:10 Screen (2560x1600/1920x1200/1680x1050/1440x900/1280x800)
Classic Wallpaper for 4:3 Screen (1600x1200/1400x1050/1280x960/1024x768)
Mobile Wallpaper for 3:4 Screen (320x480 iPhone/240x320 PDA)
PC: Right click on image and 'Set as Background' or 'Set as Wallpaper'
MAC OSX: Drag the image onto your desktop. Go to System Preferences. Then go to the Desktop icon and open it. Then drag the image into the well.
MAC OS9: Drag the image onto your desktop. Go to your Control Panel and select Appearance. Click 'set desktop' and choose your new desktop.
iPhone: Copy the image to your hard drive. Sync photos from the Photos tab in iTunes/iPhoto 4.0.3 or later.
PDA: Copy the image to your Pocket PC. Go to PDA's setting of Today screen. Then select the image.