First way, many software can download video from Youtube, but I prefer use real-one player to download video from Youtube.
User need download and install real-one player from this website http://my.real.com/
If finish you can start download video from Youtube.
If, use don't have real-one player and no want to download or install, user also can download video from youtube via on-line or via website.
Use this web to download http://keepvid.com/
Copy the url and paste to web.
Last, press button download.