js问题,谢谢大家,帮忙来看看

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>无标题文档</title>
<style type="text/css">
<!--
body,td,th {
    font-family: 宋体;
    font-size: 12px;
    
    color: #3333FF;
}
body{
line-height:20px;
}
-->
</style>
<script language="javascript">
    function switchTo(tab){
        pic = document.getElementById('pic');
        if(document.getElementById('sc')==tab){ //判断是否为企业
            qytab = document.getElementById('qytab');/ /取得企业表格对象
            qytab.style.display='none';  //不显示企业的表格
            sctab = document.getElementById('sctab'); //取得市场表格对象
            sctab.style.display='block';//将市场表格现实出来
            pic.style.background = "url(pic/bgsq.jpg) -33px 0px no-repeat"; //变换按钮图片
        }
        if(document.getElementById('rm')==tab){ //判断是否为市场
            qytab = document.getElementById('qytab');//取得企业表格对象
            qytab.style.display='none';  //不显示企业的表格
            rmtab = document.getElementById('rmtab'); //取得热门表格对象
            rmtab.style.display='block';//将热门表格现实出来
            pic.style.background = "url(pic/bgsq.jpg) -67px 0px no-repeat"; //变换按钮图片
        }
    }
</script>
</head><body>
<div align="center">
  <table width="250" border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td id='pic' width="30" background="pic/bgsq.jpg"><table width="100%" height="118"  border="0" cellpadding="0" cellspacing="0">
        <tr>
          <td height="25"><div align="center">企业</div></td>
        </tr>
        <tr>
          <td id="sc" height="26" onMouseOver="switchTo('sc');"><div align="center">市场</div></td>
        </tr>
        <tr>
          <td id="rm" height="25" onMouseOver="switchTo('rm');"><div align="center">热门</div></td>
        </tr>
        <tr>
          <td height="42" ><div align="center">交流</div></td>
        </tr>
      </table></td>
      <td><table width="100%" border="0" cellspacing="0" cellpadding="0">
        <tr>
          <td width="98%" background="../pic/sm_r12_js_r2_c2.gif">
          <div id='qytab' style="display:block;">
            <table width="100%" height="114"  border="0" cellpadding="0" cellspacing="0">
              <tr>
                <td width="40%" height="76"><img src="../pic/sp-shouyeremengengxin_1211418394176.gif" width="75" height="56"></td>
                <td width="60%" rowspan="2"><div align="left">无纺布袋掀起采购狂潮 <br>
        时尚新奇充电器 <br>
        进货稳赚独门秘籍 <br>
        创业0门槛大揭秘<br>
        无纺布袋掀起采购狂潮</div></td>
              </tr>
              <tr>
                <td>门槛大揭秘</td>
              </tr>
            </table>
        </div>
        <div id="sctab" style="display:none; ">fsdfsdfsdf</div>
        <div id="rmtab" style="display:none; ">hjfdhghfh</div>
        <div id="jltab" style="display:none; ">45345345345</div>
    
          </td>
          <td width="2%"><img src="../pic/sm_r12_js_r2_c4.gif" width="5" height="118"></td>
        </tr>
      </table></td>
    </tr>
  </table>
  <p>&nbsp;</p>
  <p>&nbsp;</p>
  <p>&nbsp;</p>
</div>
</body>
</html>上面图片是我要做的效果, 
我的js写了,但不起作用,希望好新人帮我看看!!!