树形导航问题

<style type="text/css">
<!--
    a{text-decoration:none}
    #productsmenu , #supportmenu, #contactmenu{
      display:none;
  }
-->
</style> <ul>

 <li><a id="products" href="#">[+] Products</a>
   <ul ID="productsmenu">
      <li><a href="prodlist.html">Product List</a></li>
      <li><a href="order.html">Order Form</a></li>
      <li><a href="pricelist.html">Price List</a></li>
   </ul>

 </li>

 <li><a id="support" href="#">[+] Support</a>
   <ul id="supportmenu">
      <li><a href="sforum.html">Support Forum</a></li>
      <li><a href="scontact.html">Contact Support</a></li>
   </ul>

 </li>

 <li><a ID="contact" href="#">[+] Contact Us</a>
   <ul id="contactmenu">
      <li><a href="contact1.html">Service Department</a></li>
      <li><a href="contact2.html">Sales Department</a></li>
   </ul>

 </li>
</ul>

<script language="javascript">

function Toggle(e) {

if(!document.getElementById) return;
if(!e) var e = window.event;
whichlink = (e.target) ? e.target.id : e.srcElement.id;
obj=document.getElmentById(whichlink + "menu");
visible=(obj.style.display=="block")
key=document.getElementById(whichlink);
keyname=key.firstChild.nodeValue.substring(3);
if (visible){
    obj.style.display="none";
    key.firstChild.nodeValue = "[+]" + keyname;
}else{
    obj.style.display="block";
    key.firstChild.nodeValue = "[-]" + keyname;

    }
}

    document.getElementById("products").onclick=Toggle;
document.getElementById("support").onclick=Toggle;
document.getElementById("contact").onclick=Toggle;


</script>