To post videos, simply use the YouTube tags.
|[youtube]< code to video here >[/youtube]|
Now, the code that you've got to post is the one after the "=" in the YouTube link.
For instance, let's take your video link: http://www.youtube.com/watch?v=7ynHsWoFKVk
All you have to do is to put between the YouTube tags the code in Bold.
So, to get this...
You type this...