To send to YouTube, first convert your PowerPoint to video.
Go to My stuff page http://www.authorstream.com/MyUploaded-Presentations/All
Under video dropdown click on "Convert to video" , choose free or paid video and your video will be converted to video.
If your presentation video is less than 15 mins you can directly send to YouTube, else download the video to your system and upload it manually to your account.
Go through the video to see how :- http://www.youtube.com/watch?v=PxWrGMJMVt4&feature=mfu_in_order&list=UL