If you want to download videos from YouTube why you don't try YouGrabber?
It works perfectly!
I have described it on my blog kopiowanie z youtube poprzez yougrabber
and you can translate the page with transate.google.com (http://translate.google.com/translat...F8&sl=pl&tl=en
) Its maybe not nice translation (because polish is really difficult ;-) ) but at least something at the beginning.
After I download the movie to FLV, I use this command to convert to AVI:
mencoder -oac copy -ovc lavc -o OUTPUT.avi INPUT.flv
You can use http://vixy.net
to convert online
hope this helps.