function hover(){
	$("#upper_nav").css("background-image","url('images/nav_logo_rollover.png')");
}
function no_hover(){
	$("#upper_nav").css("background-image","url('images/nav_logo.png')");
}
addLoadEvent(function() {
	$.preloadImages("images/nav_logo.png","images/nav_logo_rollover.png");
	$("#upper_nav").css("background-image","url('images/nav_logo.png')");
	$("#upper_nav").html(" ");
	$("#upper_nav").css("cursor","pointer");
	$("#upper_nav").mouseenter(function(){hover();}).mouseleave(function(){no_hover();});
	$("#upper_nav").click(function(){window.location='index.php';});
});