一个CSS问题,在IE7和FF都可以,6就不行

<!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=utf-8" /> 
<title>无标题文 </title> 
<style type="text/css"> 
body 
{ 
font-family:Arial, "宋体"; 
font-size:12px; 
border:0px; 
padding:0px; 
margin:0px; 
} 
div 
{ 
border:0px; 
padding:0px; 
margin:0px; 
background-repeat:no-repeat; 
} 
#bg_left 
{ 
margin:0px auto; 
width:197px; 
height:553px; 
background-image:url(images/left_bg.gif); 
float:left; 
} 
#bg_right_01 
{ 
margin:0px auto; 
width:120px; 
height:553px; 
background-image:url(images/right_bg01.gif); 
float:left; 
} 
#bg_right_02 
{ 
margin:0px auto; 
width:583px; 
height:553px; 
float:left; 
background-image:url(images/bg.gif); 
} 
#right_word_01 
{ 
width:450px; 
height:25px; 
font-family:"Monotype Corsiva"; 
font-size:24px; 
margin:210px 0px 0px 90px; 
color:#9da181; 
} 
#right_word_02 
{ 
width:450px; 
height:25px; 
color:#6f6f34; 
font-size:18px; 
font-family:"Impact"; 
margin:0px 0px 0px 90px; 
} 
#right_log 
{ 
width:192px; 
height:53px; 
background-image:url(images/logo.gif); 
margin:205px 0px 0px 350px; 
} 
#right_word_03 
{ 
width:225px; 
height:25px; 
color:#a5a5a3; 
font-size:18px; 
font-family:"Trebuchet MS"; 
margin:5px 0px 0px 350px; 
} 
#bg 
{ 
margin:0px auto; 
width:900px; 
margin-top:expression((screen.height-160-this.offsetHeight)/2); 
} 
.nav 
{ 
float:inherit; 
width:197px; 
height:90px; 
overflow:hidden; 
} 
.nav ul 
{ 
    margin:0px; 
    padding:0px; 
} 
.nav ul li 
{ 
padding-top:2px; 
list-style:none; 
    width:36px; 
height:90px; 
background-image:url(images/btn.png); 
background-repeat:no-repeat; 
} 
.nav ul li ul 
{ 
width:197px; 
height:90px; 
background-repeat:no-repeat; 
margin:-67px 10px 0px 0px; 
} 
.nav ul li ul li{ 
background-image:url(images/btn_011.png); 
width:193px; 
height:52px; 
line-height:52px; 
background-repeat:no-repeat; 
margin:0px 0px 0px 9px; 
display:none; 
color:#935454; 
font-size:18px; 
font-family:Impact; 
} 
.nav ul li ul li a{ 
color:#935454; 
font-size:18px; 
font-family:Impact; 
text-decoration:none; 
cursor:pointer; 
} 
.nav ul li ul:hover li{ 
display:block; 
} 
.nav_word_01 
{ 
margin:20px 0px 0px 10px; 
width:15px; 
height:45px; 
background-image:url(images/word_01.png); 
} 
.nav_word_02 
{ 
margin:0px 0px 0px 45px; 
width:100%; 
} 
</style> 
</head> <body> 
<div id="bg"> 
    <!-- 左边--> 
    <div id="bg_left"> 
      <div style="height:40px;"> </div> 
      <div class="nav"> 
          <ul> 
            <li> 
              <div class="nav_word_01"> </div> 
              <ul> 
                <li> <div class="nav_word_02">Europe </div> </li> 
              </ul> 
            </li> 
          </ul> 
      </div> 
      <div class="nav"> 
          <ul> 
            <li> 
            <div class="nav_word_01"> </div> 
              <ul> 
                <li> <div class="nav_word_02">USA North America </div> </li> 
              </ul> 
            </li> 
          </ul> 
      </div> 
      <div class="nav"> 
          <ul> 
            <li> 
            <div class="nav_word_01"> </div> 
              <ul> 
                <li> <div class="nav_word_02">South America </div> </li> 
              </ul> 
            </li> 
          </ul> 
      </div> 
      <div class="nav"> 
          <ul> 
            <li> 
            <div class="nav_word_01"> </div> 
              <ul> 
                <li> <div class="nav_word_02">Asia </div> </li> 
              </ul> 
            </li> 
          </ul> 
      </div> 
      <div class="nav"> 
          <ul> 
            <li> 
            <div class="nav_word_01"> </div> 
              <ul> 
                <li> <table cellpadding="0" cellspacing="0"> <tr> <td> <a href="EN/index.html"> <div class="nav_word_02">China <span style="font-weight:bolder;">中国 </span> </div> </a> </td> </tr> </table> </li> 
              </ul> 
            </li> 
          </ul> 
      </div> 
    </div> 
    <!-- End  --> 
    <!-- 中间--> 
    <div id="bg_right_01"> </div> 
    <!--End --> 
    <!-- 右边--> 
    <div id="bg_right_02"> 
  <div id="right_word_01">To Built The Possibility </div> 
      <div id="right_word_02">Caibro Design,&nbsp;&nbsp;Brand,&nbsp;&nbsp;Trade,&nbsp;&nbsp;Factory,&nbsp;&nbsp;Agent </div> 
      <div id="right_log"> </div> 
      <div id="right_word_03">Copyright © Caibro.Com </div> 
    </div> 
    <!--End --> 
</div> 
</body> 
</html>
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