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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>左右分栏</title>
<meta http-equiv="Content-Type" content="text/htmlcharset=gb2312">
<meta content="MSHTML 6.00.2900.2180" name="GENERATOR">
<script language="JavaScript">
//左右
function switchSysBarl(){
var imgsrc
imgsrc=document.all("makeleft").src
document.all("makeleft").src="img/menu_open.gif"
document.all("makeleft").title="显示左边的菜单"
parent.document.all("bbs_left").style.display="none"
}
else{
document.all("makeleft").src="img/menu_close.gif"
document.all("makeleft").title="隐藏左边的菜单"
parent.document.all("bbs_left").style.display=""
}
}
</script>
<link rel="shortcut icon" href="favicon.ico">
</head>
<body bottommargin="0" leftmargin="0" topmargin="0" scroll="no" rightmargin="0">
<div style="z-index: 2visibility: inheritwidth: autoheight: autofloat: left"
frameborder="0" scrolling="no" target="main">
<iframe name="bbs_left" style="z-index: 2visibility: inheritwidth: 180pxheight: 100%"
src="left.htm" frameborder="0" scrolling="no" target="main"></iframe>
</div>
<div style="background-color: #005fbdwidth: 10pxfloat: leftheight: 800pxcursor: hand
padding: 300px 0px 0px 0px" id="menuSwitch" onclick="switchSysBarl()">
<img src="img/menu_close.gif" name="makeleft" width="10" height="10" border="0" id="makeleft" /></div>
<div style="float: leftwidth: auto">
<iframe name="bbs_main" style="z-index: 1visibility: inheritwidth: 100%height: 100%" src="right.htm"
frameborder="0" scrolling="yes"></iframe>
</div>
</body>
</html>
给你的UL设置一个ID 比如 subtree,在css里面设置 #subtree{display:none} 然后在menu里面添加 onmouseover 或者 onclick 事件 建立相应函数 包含主要内容subtree.style.display=""为了兼容多个浏览器你还需要建立稍微详细点的代码,思想给你了,可以自由发挥。