Download Music

How can I download Music Videos and songs from the internet to my iphone ipod?

I just purchased an iphone 3gs, and I noticed that it came with an ipod too. So, my question is how can I download music videos, etc, to that ipod on my iphone 3gs?

You can find a video that you like in youtube (Using a PC)
and then go to this site:

http://keepvid.com/

Enter the URL of the video you want to download and wait some seconds.
Then choose save as mp4. Save it and put it on your iPhone via iTunes.

How to download music from youtube into mp3 format (using catch video)