You could use the target attribute on the link to target the iFrame.
If you have the embed links to the youtube videos, you can do something like this:
<p><a href="http://www.youtube.com/embed/Q5im0Ssyyus" target="someFrame">Charlie 1</a></p>
<p><a href="http://www.youtube.com/embed/QFCSXr6qnv4" target="someFrame">Charlie 2</a></p>
<p><a href="http://www.youtube.com/embed/eaCCkfjPm0o" target="someFrame">Charlie 3</a></p>
<iframe name="someFrame" id="someFrame" width="560" height="315"></iframe>
Live demo: [URL=“http://jsfiddle.net/GeekyJohn/GH5QG/”]http://jsfiddle.net/GeekyJohn/GH5QG/
Of course if for some reason you need to use JavaScript, then you could simply change the source of the iframe.
in jQuery parlance this would only be a few lines:
$(document).ready(function(){
$("a").click(function(e) {
e.preventDefault();
$("#someFrame").attr("src", $(this).attr("href"));
})
});