怎么才能像IE菜单一样让菜单被点击以后，才显示下拉菜单？（40分奉送）

Question

<script>
function goto()
{
form1.action=event.srcElement.innerHTML+".jsp";
form1.submit();
}
</script>
<form name=form1>
<div onclick="sub.style.display='block'" style="background:yellow;width:100">menu</div>
<div id=sub style="display:none" onmouseover="this.style.display='block';this.style.cursor='hand'" onmouseout="this.style.display='none'" style="background:lightgreen;width:100">
<table width=100%><tr onclick=goto()><td>sub1</td></tr>
<tr onclick=goto()><td>sub2</td></tr>
<tr onclick=goto()><td>sub3</td></tr>
</table>
</div>
</form>