To set beautiful Bing pictures as your Windows 7 desktop background, download the custom theme file, install it on your Windows 7 computer and optionally modify the setting. A blog post outlines the three steps in detail.
If you are curious about how the custom theme works behind the scenes, and how the Bing images are downloaded to your computer via an RSS feed, read this blog post. Amazing!
For Windows XP users: the custom theme will not work on XP. However, you still can enjoy Windows 7 themes on your XP if you like. Watch this interesting youtube video to find out how.
Note: A Windows desktop theme is a combination of pictures, colors, and sounds on your computer. It includes a desktop background, a screen saver, a window border color, and a sound scheme. Some themes might also include desktop icons and mouse pointers. Windows comes with several themes including Aero themes you can choose from. Click here to learn more about Windows theme and how to change and customize your desktop theme. You can download additional themes from Microsoft.com and other web sites.