一段超难度的JS滚动代码?大家帮我看看,怎么不动呀?

<div class="tuijian_cont_son" style="margin-top:5px;">
 <!--中间滚动图片的显示-->
 <div id="demc">
 <table width="100%" border="0" cellspacing="0" cellpadding="0" >
  <tr>
<td id=dema>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td>
ddddddddddddddddddddddddddddd
</td>
</tr>    
</table>
 </td>
 <td id=demb></td>
   </tr>
 </table> 
 <script language="javascript" type="text/javascript">
            var dema=document.getElementById('dema')
var demb=document.getElementById('demb')
var demc=document.getElementById('demc')
var speed=40                                                                            
demb.innerHTML=dema.innerHTML                                                       
function Marquee(){                                                              
if(demb.offsetWidth-demc.scrollLeft<=0)                                                   
demc.scrollLeft-=dema.offsetWidth                                                    
else{                                                                                
demc.scrollLeft++                                                                       
}                                                                                     
}                                   var MyMar=setInterval(Marquee,speed)                                                    
demc.onmouseover=function() {clearInterval(MyMar)}                                           
demc.onmouseout=function() {MyMar=setInterval(Marquee,speed)}                   
</script>
 </div>  

 <!--中间滚动图片的结束--> 
<div id="clear" class="clear"></div>
</div>
 <!--横向滚动结束-->