Another way to download a youtube video onto your hard drive for use in school (in my school nothing hosted on youtube will play!).
First I went to Zamzar and told it I wanted to download a video. I told it I wanted it to be a .mov file and gave it my address. Then I went to the video I wanted and copied the URL from the address bar. I removed the word "watch" to make it in the same format as the zamzar example.
The whole process took less than a minute and I captured the process using JING*. Here's the JING video:
Several minutes later I received the email from Zamzar and clicked the link to download my .mov video.
Anyhow, I thought you'd be interested. Let me know if it works for you or not.
*JING is a freeware tool for Mac/Windows/Linux. It captures images and videos of your screen, and then can automatically upload them to screencast.com (a free video streaming site). So all I did, once I had set up my screencast account, was tell JING to film my firefox window, then share it. A minute later JING said "the URL for your recorded video is now copied to your clipboard" and I pasted it into the email above. It's pretty slick.