To download any Youtube clip in .mp4 format just add "22" after "Youtube" in the address.
ex:
http://www.youtube22.com/watch?v=iBsTTtgI88g
To capture cam sessions you'll need screen recording software like Hypercam.
http://www.hyperionics.com/hc/
You simply highlight the region of the screen you want captured and it will record it whatever it is. You need a fast .avi codec and fast computer to get good (non choppy) results though