In the RC build of Windows 7, you can see a number of new themes, for example the “Architecture” theme. This theme is comprised of six architectural photos which cycle on the desktop background, a complementary “Twilight” window color and the “Cityscape” sound scheme which was inspired by the sounds of an urban jazz club. You can apply, create, and save themes directly from within the Personalization Control Panel in Windows 7. When you create a theme for Windows 7, Windows 7 collects desktop backgrounds, sounds, mouse pointers and icons and puts it into an .themepack file. That file can be shared and them theme can then be applied on another Windows 7 PC.
Full Article: E7 blog