Ripping videos from YouTube using Ubuntu is a pretty easy process. First of all download youtube-dl from the Universe repository.
sudo apt-get install youtube-dl
Next get the URL of the video you wish to download.
youtube-dl http://
This will download the video you require in Flash Video (*.flv) format. If you want to convert this to MPEG then you will first need to install ffmpeg.
sudo apt-get install ffmpeg
Then get ffmpeg to do the conversion.
ffmpeg -i input.flv output.mpg
Incidentally I quite like using Tilda to manage consoles - I'd reccomend you take a look too.
