A few others in another thread found this information useful.
You can emulate the "Windows Desktop Backgrounds" Slide Show using your personal wallpaper collection.
If you would like to organize your desktop wallpaper collection into separate folders, but include them all in a Desktop Slide Show, the Windows 7 Library function can be used.
1) Place your wallpaper collection(s) into one or more folders of your choosing.
2) Create a new LIBRARY. For example "My Desktop Wallpapers"
3) Add each folder created in Step 1 to the "My Desktop Wallpapers" library.
4) Go to CONTROL PANEL>PERSONALIZATION>DESKTOP BACKGROUND
5) Click BROWSE>LIBRARIES and select the "My Desktop Wallpapers" library created in Step 2.
6) Select the desktop wallpapers you want included in your slide show. Notes:
The folder created in Step 1 must contain at least 1 picture before they will appear in Step 6.
The folder view in Step 6 is "flat" and no subdirectories will be shown. Even though a library may include subdirectories, only the immediate folder reference specified in the library will appear in Step 6.
The folder list in Step 6 displays the full folder path specification. The folder list in the "Windows Desktop Backgrounds" lists the folder name only. If you know where the Windows 7 registry/configuration setting to control this behavior is located, please let me know.