There are a few beautiful themes and Wallpapers hidden in windows 7 that you can use. The idea by Microsoft was to Install only that theme which matches your location i.e. if you live in USA United States theme is installed automatically. The other themes that are there and not installed by default are Australia, South Africa, Canada, and United Kingdom. The themes contain 1920 x 1200 resolution wallpapers from the respective countries. Just open explorer and type
in the address bar , hit enter. It will open the folders containing Wallpapers and themes.