To Create Picture Screensaver from PowerPoint SlidesCreate an empty folder in "My Pictures" or any other folder on your hard-drive. Now open the PPT or PPS file in Microsoft PowerPoint and click File -> Save As. Select "JPEG" in the file-type drop-down and click "Export every slide."
See: Extract Sounds, Images from PowerPoint Files
Your Powerpoint presentation is now available as JPG images in one folder. Right click the deskop -> Properties -> Screensaver and select the "My Picture Slideshow" screensaver. Browse to the folder where you save the PPT and you're done. [Disable "Use Transition Effects" for best results]
To Upload PowerPoint Presentations to YouTubeThere are two option here - either run the PowerPoint as a full-screen slideshow and capture the desktop using some screen recording software OR make a movie from PowerPoint slide images. We'll use the latter approach though you won't see the animations or transitions in the PowerPoint movie.
Start a new project in Windows Movie Maker and import (Ctrl+I) the entire folder of images in the timeline that we created in the Screensaver hack above.
Reverse trick: How to Embed Youtube Videos in PowerPoint Presentations
Switch to storyboard in WMM, drag all the image to timeline and click Tools->Options->Advanced. Now change the picture duration and transition duration (keep this to a minimum value). Finally save the movie file - your PowerPoint is now a video.
You may either use Windows Movie Maker to add music and narration to your PowerPoint movie or a commercial app like Camtasia Studio.