Youtube vids are auto added into the post when you post it. They wont show however in the preview
http://www.youtube.com/watch?v=RfuU9sEQ6Us
http://www.youtube.com/watch?*feature=player_embedded&*v=RfuU9sEQ6Us
as you can see above, just remove the part in the *'s from the youtube link and it will be automatically added into the post