Microsoft released the Windows 8 Consumer Preview not to long ago. They even released there first Windows 8 theme as well called Nightfall and Starlight Panoramic. This theme contains beautiful dual screen wallpapers. These wallpapers are supposed to work with two monitors that have the same resolution. If you are running the Consumer preview you can download this theme from Microsoft’s Personalization Gallery or snag them from below.
Frist Windows 8 Theme NightFall and Starlight Panoramic