You can delete the div "usplayer" content and rewrite the embedding code with new link, with jQuery it's very easy:

PHP Code: 
$(".links a").click(function(){
embed = $('<object id="jwplayer786" class....>....<param name="FlashVars" value="'+$(this).href()+'" />'); //the same embedding code with just changin the FlashVars value with the clicked link...
$("#usplayer").html(embed);
return 
false//to stop the a click event
});