the jquery code containing the vimeo player is below
$("modal-nofooter").addEvent("click", function(e){
e.stop();
var SM = new SimpleModal({"hideFooter":true, "width":710});
SM.show({
"title":"Vimeo video",
"model":"modal",
"contents":'<iframe src="http://player.vimeo.com/video/26198635?title=0&byline=0&portrait=0&color=824571" width="680" height="382" frameborder="0" webkitAllowFullScreen allowFullScreen></iframe>'
});
})
Maybe change the 'src' attribute of the iframe to the youtube video you want? I'm not familiar with the simplemodal plugin, but right off the top of my head, that sounds about right.