If your embedded iframe YouTube videos are covering up your Drop Down Navigation Menu, try adding the following snipit to your iframe code:
?wmode=opaque
Old code: <iframe width="467" height="380" src="http://www.youtube.com/embed/T6MhAwQ64c0" frameborder="0" allowfullscreen></iframe>
New code: <iframe width="467" height="380" src="http://www.youtube.com/embed/T6MhAwQ64c0?wmode=opaque" frameborder="0" allowfullscreen></iframe>
If you are using Google Chrome & the new code isn't working, trying changing "opaque" to "transparent"