How to download videos from YouTube

I recently saw this little ad on anorexia. I’ll be teaching anorexia at college soon. Although it is great that we can show the internet in class through the computer projectors it is frustrating that videos are blocked. I found it on YouTube and thought that it was a pity that YouTube doesn’t let you download the videos. 'Is there another way?' I asked. Well a colleague showed me keepvid.com. If you copy the address of your video into this site then it will save it for you. The downside is that you need to install the video player from keepvid's site in order to watch the video. So though this will enable me to play any YouTube video when I’m offline on my laptop I still can’t use it at college because the college system won’t let me install the player. Oh well! Never mind.