Help with downloading vids from Youtube

[Infernal Dave]

Im not sure if this is the appropriate forum, but I need some help. I have heard that you can download peoples videos, and keep them yourself from Youtube.com
I need/want this because I want to save some videos on my Nintendo ds.
(I bought this thing called Games 'n Music where you can upload Videos/movies, mp3/songs, and games from the producers site. My brother downloaded an episode of Avatar: the last airbender on the memory card, but I want to know myself.)

My brother is busy alot, so I can't disturb him. So does anyone know how to "keep" videos from youtube?

 

[BGD]

I use Replay Media Catcher it saves them as flv files. All you have to do is play the video and it automatically starts downloading except you have to pay for the program =/