Zam's method shows you how to LINK to a youtube vid. To EMBED, you need to add code like this
<iframe width="560" height="315" src="http://www.youtube.com/embed/vEo8BHnTBQs" frameborder="0" allowfullscreen></iframe>
for this vid:
http://youtu.be/vEo8BHnTBQs
which actually does not seem to work in the forum post! The forum posts have limited html capacity. The above would work if you put it in your blog - or something like that.
If you can point us in the direction of a POST that has a youtube vid embedded, I will take a look and see if I can get the code they used.