There is a big difference between inserting a video into a PowerPoint and linking a video to a PowerPoint. You can link a video file or link to a website that contains the video.
Instructors have been using YouTube Videos in their presentation to show examples of what to do and what not to do. I would recommend asking permission of the producer to use the video to limit the liability and potential violation of copyright laws.
Click on this link to view a printable PDF on how to take YouTube videos and link them into your PowerPoint presentations by capturing the video from YouTube and saving the video as a video file (MPEG, AVI) on your computer.
For those of you that teach Fair Housing this would be a good one to grab.
I will be teaching an advance PowerPoint session at Midyear Convention in Washington D.C. if you can make the ABR recertification. It will cover mainly PPT 2007 and multimedia presentations.