Dem posted this ages ago. I think it should help, at least as a starting point, if not as your final answer.
If you want to download those videos
from "you tube" and save them in your pc
you can use this tool:
http://keepvid.com/
The files are saved as .flv
Here's a converter .flv to other file types
http://vixy.net/
(You can use the page or download the application version).