How do I download from youtube?

okay so there is this video on youtube http://www.youtube.com/watch?v=VHnvhQIyudo&feature=related I am absolutely obsessed with it and I can't get it on iTunes so I am trying to figure out a way to download the video onto my iTunes so I can listen to/watch it on my iPod. Please help by giving me a walk through or something please don't just give me a link though I HATE IT when people do that because it doesn't help. Thanks!