Windows XP's default background is entitled bliss. The picture itself is in fact a bitmap file. By making it a JPG file it will become much smaller in size and cut back load time.

To do this, follow the next steps:

1. Go to C:\Windows\Web\Wallpaper.
    
2. Open Bliss with Microsoft Paint.
    
3. Save for example as "bliss2.jpg" (be sure to change the format in which to save it in).
    
4. Change Background to Bliss2.