//menu
$(document).ready(function(){

 $("li.mainlevel").hover(function(){
$("ul",this).slideDown("fast");//$("ol",this): 寻找this中的ol.
},function(){
$("ul",this).slideUp("fast");
});

$("li.mainlevel").hover(function(){
    $("#Products",this).css({"background-image":"url(./images/nav2.gif)"});
},function(){
    $("#Products",this).css({"background-image":"url(./images/nav1.gif)"});
});
  
});