Steps to follow:
1. Determine the name of the screen saver you want to use. Click “Start,” then “Control Panel.” In the search box, enter “screen saver.” When the results appear, click “Change Screen Saver.” Scroll through the list that appears to find the correct one, and write down the exact name.
2. Click the “Start” icon. In the search bar, type “cmd” and hit “Enter.” This opens the command prompt.
3. Enter the exact name of the desired screen saver in the command prompt box, followed by “/p65552.” For instance, if the screen saver is named “waterfalls,” you must type “waterfalls.scr/p65552.” Hit “Enter” when you are finished.
4. Hit “Ctrl,” “Alt” and “Delete” together to open Task Manager, which allows you to regain control over your desktop. Click on the Task Manager if your task bar at the bottom of the screen disappears.
5. Remove the screen saver from the desktop by pressing “Alt” and “F4″ together.
Obtained from: http://windows7net.com/windows-7-guides/how-to-set-screensaver-as-desktop-wallpaper/
