If you have installed Windows 7 beta on your PC, then you might also be interested in installing free Windows 7 themes, Wallpapers and gadgets which are provided by Microsoft. These are official themes and gadgets from Microsoft, so you can go ahead and install them. All the themes, wallpapers and gadgets are available for download free of cost.
When you download any theme, a file with the extension .themepack will be downloaded. Simply double click on the downloaded theme file, the theme will be automatically installed.
The wallpapers available are all high resolution ones and only a few numbers are available as of now. The gadgets can be downloaded from Live Gallery.