Microsoft in a new blog post on the Windows Experience Blog clarified the company’s intention to go forward with the way themes have been provided recently. Windows 7 users may remember the changes the company made to themes in their operating system. The fundamental change made themes distributable, and as a result incompatible with previous Windows operating systems.
While it it possible to extract the theme contents to make use of the wallpaper images they contain, there is no option to install the themes directly in Vista, XP or another pre-Windows 7 operating system.
Themes get new improvements and features in Windows 8, namely auto color settings, panoramic theme support and better dual monitor support in general.
The auto coloring feature changes the color of the desktop class and taskbar color to the dominant color of the background image. You can read more about the feature here: Windows 8 Aero Auto-Colorization
The feature is optional though, and Windows 8 users who prefer to stick with a select color can do so as well.
Panoramic themes are themes optimized for dual monitor systems. They are designed to display a panoramic image on both monitors. They can be installed on single-monitor systems as well, in which case the images will be cropped on the left and right so that only the center will be visible.
The second dual monitor feature is support for different wallpaper images if a regular-sized theme is installed. Windows 8 will automatically display two wallpaper images from the theme instead of the same image on both monitors.
Because of those changes, Windows 8 themes are not compatible with Windows 7 operating systems. The other way round works though. Windows 8 users can install Windows 7 themes on their system just fine.
Check out the full post here.