请问在下面的的代码中如何修改可以实现点击后改变图片吗?还请各位大师多多指教,拜拖哪....
    <link   rel= "stylesheet "   type= "text/css "   href= "css.css ">  
  <base   target= "right ">  
  <style   type= "text/css ">  
  <!-- 
 body   { 
 	margin-left:   0px; 
 	margin-top:   0px; 
 	margin-right:   0px; 
 	margin-bottom:   0px; 
 } 
 .STYLE1   {color:   #000000} 
 -->  
  </style>  
  <script   language= "javascript ">  
 function   showdiv(div_id,img_i) 
 { 
 if(document.all.item(div_id).style.display== "block ") 
       { 
                document.all.item(div_id).style.display= "none "; 
 	   img_i.src= "pic/P1.gif "; 
 	   return   true; 
       } 
 else 
       { 
                document.all.item(div_id).style.display= "block "; 
 	   img_i.src= "pic/M1.gif "; 
 	   return   true; 
       } 
       return   false;       
 } 
  </script>  
  <body>  
  <table   border= '1 '   cellpadding= '0 '   cellspacing= '0 '   style= 'border-collapse:   collapse '   bordercolor= '#FF9900 '   width= "95% ">  
        <tr>  
              <td   width= "100% "   height= "28 "   align= "center "   bgcolor= "#FFFF00 ">  
              <a   href= "index.asp "   target= "_top "   class= "STYLE1 ">                 <b>    返回论坛首页 </b>  </a>  </td>  
        </tr>  
  </table>    
  <table   border= '0 '   cellpadding= '0 '   cellspacing= '0 '   style= 'border-collapse:   collapse '   bordercolor= '#FF9900 '   width= "95% "   >  
  <tr>  
  <td   height= "1px ">   </td>  
  </tr>  
  </table>    
  <table   border= '1 '   cellpadding= '0 '   cellspacing= '0 '   style= 'border-collapse:   collapse '   bordercolor= '#FF9900 '   width= "95% "   >    
        <tr>  
              <td   height= "22 "   bgcolor= "#FFFF00 ">              <font   color= "#FFFFFF ">  <b>   <img   src= "pic/P1.gif "   alt= "点击下拉 "   width= "20 "   height= "20 "   align= "absmiddle "      language= "javascript "   onClick= "showdiv( 'div2 ', 'img2 '); "   name= "img2 "   id= "img2 ">   <span   class= "STYLE1 "> 论坛管理 </span>  </b>  </font>              </td>  
        </tr>  
  </table>  
  <div   id= "div2 "   style= "display:none ">  
  <table   border= '1 '   cellpadding= '0 '   cellspacing= '0 '   style= 'border-collapse:   collapse '   bordercolor= '#FF9900 '   width= "95% "