Heya~
Oh gosh I had some much trouble figuring out how to do this at first. I'm experienced? d'aww Well, basically..
You go to your User CP > Edit Your Details...
Then scroll down too Youtube Url.
Then, get your youtube url... Well, I'll demonstrate.
http://www.youtube.com/watch?v=DeOYItVizIc <- The full url.
We want: watch?v=DeOYItVizIc BUT... That's not all, that wont work. What you do is... Remove the watch? part so you get v=DeOYItVizIc ... Then, change the = to a /
The finished product would be v/DeOYItVizIc -- Then, it should work.
I dont recall seeing any threads on this matter, so I hope it helps! :D