This is a great tutorial from e-How about adding video clips to your PowerPoint presentation:
On another note, frequently people ask me how to download YouTube videos to embed in their presentations. You can find out what I have learned at this link. It has the top 23 tools you can use for downloading YouTube videos and converting them to some other format beside the .flv format.
Or you can watch this video as well: (I would click the player to get the text directions for this video tutorial).
nan @ brainybetty :)