Hi
You can embed a youtube video in a custom-html module using embed code
Example :
<object data="http://www.youtube.com/v/NnD2n_NBGMg?fs=1&hl=en_US&autoplay=0&showinfo=0&rel=0" type="application/x-shockwave-flash" width="310" height="199"><param name="movie" value="http://www.youtube.com/v/NnD2n_NBGMg?fs=1&hl=en_US&autoplay=0&showinfo=0&rel=0" /><param name="wmode" value="transparent" /></object>
First to create a new custom-html module disable your default editor from global configuration add code save and then reenable default editor.
Then publish your module in the desired position.