我在IE6跟IE7浏览，它的位置不相同的。
听说是定位问题，请问要怎样解决呢？
<!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>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
<style type="text/css">
*{
font-size:12px;
font-family:Tahoma, Geneva, sans-serif;
}
#nav a{
display:block;
width:80px;
}
#nav{
margin:0;
padding:0;}
#nav li{
float:left;
text-align:center;
}
#nav li a{
color:#FFF;
background:#000;
height:25px;
}
#nav li a:hover{
color:#000;
background:#999;
}
#nav li ul{
list-style-type:none;
margin:0px;
padding:0px;
display:none;
}
#nav li ul li{
float:none;
}
#nav li ul li a{
width:80px;
height:25px;
background:#333;
color:#90F;
}
#nav li ul li a:hover{
background:#999;
color:#F00;
}
#ddss{
position:absolute;
top:40px;
left:9px;
width:950px;
height:20px;
background:#CCC;
margin:5px 0 0 0;
z-index:1
}
.yy{clear:both;height:10px;line-height:1px;font-size:1px;}
#ddst{
position:absolute;
top:10px;
left:9px;
margin:5px 0 0 0;
z-index:2
}
</style>
</head>
<body>
<div id="ddst">
<ul id="nav">
<li onmouseover="show('nav_1');" onmouseout="hide('nav_1')" ><a href="#">一</a>
<ul id="nav_1">
<li><a href="#">1-1</a></li>
<li><a href="#">1-2</a></li>
<li><a href="#">1-3</a></li>
</ul>
</li>
<li onmouseover="show('nav_2');" onmouseout="hide('nav_2')" ><a href="#">二</a>
<ul id="nav_2">
<li><a href="#">2-1</a></li>
<li><a href="#">2-2</a></li>
<li><a href="#">2-3</a></li>
</ul>
</li>
<li class="yy"></li>
</ul>
</div>
<div id="ddss">-------------------被挤走了，怎么办？？？---------------------------------
</div>
<script type="text/javascript">
function show(id){
document.getElementById(id).style.display='block';
}
function hide(id){
document.getElementById(id).style.display='none';
}
</script>
</body>
</html>