If I may, here is a way to run a video as screensaver. It is a little different than in Vista.
In Windows 7 you have to go via Windows Live Photo Gallery. If you do not have it yet on your system, download it from Windows Live Essentials
http://download.live.com/?wa=wsignin1.0
Then do the following steps:
· Open Live Essentials Photo Gallery
· Click on File
· Click on > Screen Saver Settings (This will open the Screen Saver Settings)
· Browse to your folder with the video and open it (OK)
· In the Use this theme list box, select Album
· Then do Save
· Now run Preview and see whether it works
Remind you that the video format must be .wmv. If you have another format, convert it with Format factory
http://www.formatoz.com/