Maybe this is what your talking about, you can download the video in Avi DivX. I found it a while back. http://vidtaker.com/
You can use keepvid.com to download the flv from YouTube (and heaps of other video sites). Then either watch the flv using Media Player Classic (free), or convert the flv to something else using Total Video Converter (not free).
Thx guys rep added. I d tried keepvid.com and downloaded but the file didnt work in Media Player. firefox plugin was ok but sound quality is very bad.
I think vixy is who you are looking for. http://vixy.net/ allows you to download video off of youtube (and other sites) as a variety of formats so you can watch it on your computer, ipod, etc. It's pretty nice.