用js控制div的显示和隐藏。
div.style.display = "none" 和 div.style.display = "block"。
页面代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript">
var count = 0; //做计数器
var limit = new Array(); //用于记录当前显示的哪几个菜单
var countlimit = 1; //同时打开菜单数目，可自定义
function expandIt(el) {
obj = eval("sub" + el);
if (obj.style.display == "none") {
obj.style.display = "block"; //显示子菜单
if (count < countlimit) {//限制2个
limit[count] = el; //录入数组
count++;
}
else {
eval("sub" + limit[0]).style.display = "none";
for (i = 0; i < limit.length - 1; i++) { limit[i] = limit[i + 1]; } //数组去掉头一位，后面的往前挪一位
limit[limit.length - 1] = el;
}
}
else {
obj.style.display = "none";
var j;
for (i = 0; i < limit.length; i++) { if (limit[i] == el) j = i; } //获取当前点击的菜单在limit数组中的位置
for (i = j; i < limit.length - 1; i++) { limit[i] = limit[i + 1]; } //j以后的数组全部往前挪一位
limit[limit.length - 1] = null; //删除数组最后一位
count--;
}
}
</script>
</head>
<body>
<div id="main1" onclick="expandIt(1)">
<table width="170" height="24" border="0" cellpadding="0" cellspacing="0">
<tr style="cursor: hand;">
<td width="26">
</td>
<td class="SystemLeft">
企业信息
</td>
</tr>
</table>
</div>
<div id="sub1" style="display: none">
<table width="160" border="0" cellspacing="0" cellpadding="0">
<tr>
<td width="36" height="22">
</td>
<td class="SystemLeft">
<a href="AboutList.asp" target="mainFrame" onclick='changeAdminFlag("企业信息列表")'>企业信息列表</a>
</td>
</tr>
<tr>
<td width="36" height="22">
</td>
<td class="SystemLeft">
<a href="AboutEdit.asp?Result=Add" target="mainFrame" onclick='changeAdminFlag("添加企业信息")'>
添加企业信息</a>
</td>
</tr>
</table>
</div>
<div id="main2" onclick="expandIt(2)">
<table width="170" height="24" border="0" cellpadding="0" cellspacing="0">
<tr style="cursor: hand;">
<td width="26">
</td>
<td class="SystemLeft">
新闻资讯
</td>
</tr>
</table>
</div>
<div id="sub2" style="display: none">
<table width="160" border="0" cellspacing="0" cellpadding="0">
<tr>
<td width="36" height="22">
</td>
<td class="SystemLeft">
<a href="NewsSort.asp?Action=Add&ParentID=0" target="mainFrame" onclick='changeAdminFlag("新闻类别")'>
新闻类别</a>
</td>
</tr>
<tr>
<td width="36" height="22">
</td>
<td class="SystemLeft">
<a href="NewsList.asp" target="mainFrame" onclick='changeAdminFlag("新闻列表")'>新闻列表</a>
</td>
</tr>
<tr>
<td width="36" height="22">
</td>
<td class="SystemLeft">
<a href="NewsEdit.asp?Result=Add" target="mainFrame" onclick='changeAdminFlag("添加新闻")'>
添加新闻</a>
</td>
</tr>
</table>
</div>
<div id="main3" onclick="expandIt(3)">
<table width="170" height="24" border="0" cellpadding="0" cellspacing="0">
<tr style="cursor: hand;">
<td width="26">
</td>
<td class="SystemLeft">
产品展示
</td>
</tr>
</table>
</div>
<div id="sub3" style="display: none">
<table width="160" border="0" cellspacing="0" cellpadding="0">
<tr>
<td width="36" height="22">