A awesome website for it is vixy.net. It converts any youtube video to divx, mp4 etc etc. You can also download a program that goes onto your computer which i find works better than the onsite one because they get some errors because its always got high traffic.
Yes, get firefox and then get the extension Video DownloadHelper. I do not use this no need for it, I think that it saves the videos as .flv like most video down loaders and if you want it as a .avi .wmv you do need a converter FF Extension below. https://addons.mozilla.org/en-US/firefox/addon/3006
Heres a REALLY good program. Its called Youtube Downloader and all you do is find the video on Youtube and load the program, then copy the link of the youtube page to the program and it downloads it in a flash file. Then use the inbuilt converter to change the file to wmv or mp4 or whatever. I found this extreemely usefull. http://youtubedownload.altervista.org/
if u got a mac u need isquint then follow the instructions i made a cool halo movie thing im gonna post soon
You could use the most obvious of them all, http://www.downloadyoutubevideos.com/. I've used it many times and I just use 3GP Video Converter.
lol I suppose that link is obvious, I wonder if I went to halo4.com... Anyway, try mine cos it does it all in one.
How is this random pointless thread constantly staying bumped at the top of the page.... that should tell you all something about this section of the forums... lulz.