Saw a nice little program today for downloading videos from Youtube and converting them from the flv format, to pretty much all the other main ones. Avi, mp4, mov, mp3, wav. Yes you can extract the music from the video too.
Now since a lot of you on here have ipods, and perhaps a few have other decent media players, I'd link you to it.
It's very simple to use, it's like a new browswer (what you use to look at the internet) and you go to youtube, see a video you like? Click the very large "Download" button.
There are preferences to where you want to save the downloads and conversions, and they are all defaulted to the usual My Documents places.
I'd recommend it, and so does my wife.