Alternatively...
using the spitfire video as an example, the URL of the actual YT page is http://www.youtube.com/watch?v=Wpq4Tu2NnrQ
Take the code AFTER the = sign (giving you Wpq4Tu2NnrQ)
and insert it between the YT code
Therefore you will be left with
[yt ]Wpq4Tu2NnrQ[/yt] IMPORTANT -...