First off, read this article here about using Youtube in the classroom. If you are still interested comeback here to learn about downloading video from Youtube (Yes, legally).
OK, you’re back now? Good. Saving video from Youtube is pretty easy. In fact, there are a lot of different ways to do it. I’m going to recommend using Keepvid.com.
First step, find a video on Youtube.
Ctrl+Click (or Right Click) on the Download (MP4) and save to your computer. Once it downloads you will have your video to play whenever and where ever.
You can take the video and then embed it into a PowerPoint presentation you are planning to do as well.