If you go to the "Info" box on the right side of the YouTube page you want to display.
You will see "Embed" and "URL" codes.
Copy the "URL" code into your BePositive.ie post that you are creating and delete everything from the = sign to the left.
Example:
http://www.youtube.com/watch?v=N7IZmRnAo6s now becomes N7IZmRnAo6s
Now pop N7IZmRnAo6s in between your 'youtube' code - Preview . . . and your good to go!!
The Positive Team