When posting videos, just paste the full URL (address) from YouTube into your post. For example, if you were going to post a video of the Village People's YMCA video you would paste the URL
http://www.you.tube.com/watch?v=CS9OO0S5w2k into the post. The system renders it, if it's allowed to be embedded, into the video (you may not see it in the preview).
[ame="http://www.youtube.com/watch?v=CS9OO0S5w2k"]YouTube- YMCA[/ame]