Grabbing video from the web is a fraught business, as the default format of the streaming video sites, flv, is not very usable and so you need a downloader.
My preferred solution is Save2PC (www.save2pc.com)
The latest version also supports Vimeo (www.vimeo.com) (where my videos can be found at http://www.vimeo.com/frsimon )
This makes it brilliant for downloading everything, from YouTube to TeachersTV (for Lou) to Vimeo and Google and even (ahem) sites that you wouldn’t want to (which which I bet is a facility which makes this kind of program a money spinner).
Online, a free and okay version is at http://vixy.net/ but I personally prefer and recomend Save2PC, even though the Pro version costs $35, I reckon it’s worth it.