一个简单的拖放问题
<!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>  
  </head>  
  <style>  
 .aaa{   list-style:none;   padding:0px;   margin:0px;} 
 .aaa   li{   width:50px;   height:50px;   border:1px   solid   #000000;   line-height:50px;   text-align:center;   float:left;   margin:5px;} 
  </style>  
  <body>  
  <ul   class= "aaa ">  
        <li> 1 </li>  
        <li> 2 </li>  
        <li> 3 </li>  
        <li> 4 </li>  
  </ul>  
  </body>  
  </html>    
 这样的   几个方块   如何实现    
 http://www.google.com/ig?hl=zh-CN      这样的拖动效果?
------解决方案-------------------- <!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 " lang= "gb2312 ">    
  <head>    
  <title>  代码实例:拖动对象 Drag Object (兼容:IE、Firefox、Opera ... ) </title>    
  <meta http-equiv= "content-type " content= "text/html; charset=gb2312 " />    
  <meta name= "editor " content= "枫岩,http://www.cnlei.com ">    
  <meta name= "keywords " content= "代码实例:拖动对象 ">    
  <meta name= "description " content= "最简短的拖动对象代码实例演示 ">    
  <style>    
 .aa {position:relative;cursor:move;}   
  </style>    
  <script language= "javascript ">    
  <!--   
 // Author:  Unkonw   
 // Modify:  枫岩@CnLei.com   
 var ie=document.all;   
 var nn6=document.getElementById&&!document.all;   
 var isdrag=false;   
 var y,x;   
 var oDragObj;     
 function moveMouse(e) {   
  if (isdrag) {   
  oDragObj.style.top  =  (nn6 ? nTY + e.clientY - y : nTY + event.clientY - y)+ "px ";   
  oDragObj.style.left  =  (nn6 ? nTX + e.clientX - x : nTX + event.clientX - x)+ "px ";   
  return false;   
  }   
 }     
 function initDrag(e) {   
  var oDragHandle = nn6 ? e.target : event.srcElement;   
  var topElement =  "HTML ";   
  while (oDragHandle.tagName != topElement && oDragHandle.className !=  "aa ") {   
  oDragHandle = nn6 ? oDragHandle.parentNode : oDragHandle.parentElement;   
  }   
  if (oDragHandle.className== "aa ") {   
  isdrag = true;   
  oDragObj = oDragHandle;   
  nTY = parseInt(oDragObj.style.top+0);   
  y = nn6 ? e.clientY : event.clientY;   
  nTX = parseInt(oDragObj.style.left+0);   
  x = nn6 ? e.clientX : event.clientX;   
  document.onmousemove=moveMouse;   
  return false;   
  }   
 }   
 document.onmousedown=initDrag;   
 document.onmouseup=new Function( "isdrag=false ");       
  </script>    
  </head>       
  <body >      
  <img src= "http://webdesign.chinaitlab.com/UploadFiles_8014/200612/20061202115506895.gif " class= "aa " />    
  <img src= "http:/