JavaScript 做交换图片？

JavaScript做图片交换！

就是 导航栏原有的图片变成鼠标滑过和点击之后的图片，而且右边div中有张图片是随着导航改变而改变的！怎么做 ？

<script language="javascript" type="text/javascript">
//<![CDATA[
var _t1 = 0; //打开页面时等待图片载入的时间，单位为秒，可以设置为0
var _t2 = 5; //图片轮转的间隔时间
var _tnum = 4; //焦点图个数
var _tn = 1;//当前焦点
var _tl =null;
_tt1 = setTimeout('change_img()',_t1*1000);
function change_img(){
setFocus(_tn);
_tt1 = setTimeout('change_img()',_t2*1000);
}
function setFocus(i){
if(i>_tnum){_tn=1;i=1;}
_tl?document.getElementById('focusPic'+_tl).style.display='none':'';
document.getElementById('focusPic'+i).style.display='block';
_tl=i;
_tn++;
}
//]]>
</script>
<!--焦点图1开始 标题13字 说明30个字-->
<div id="focusPic1">
<a href="http://www." class="i_photo_a" target="_blank">
<img src="images/01.jpg" /></a>
<h1><a href="http://www./" target="_blank">精致双眼皮</a></h1>
<div id="index_page">
<strong>1</strong>
<a href="javascript:setFocus(2);">2</a>
<a href="javascript:setFocus(3);">3</a>
<a href="javascript:setFocus(4);">4</a>
</div></div>
<!--焦点图1结束-->
<!--焦点图2开始 标题13字 说明30个字-->
<div id="focusPic2" >
<a href="http://www..com/" class="i_photo_a" target="_blank">
<img src="images/02.jpg" /></a>
<h1><a href="http://www..com/" target="_blank">完美丰胸</a></h1>
<div id="index_page">
<a href="javascript:setFocus(1);">1</a>
<strong>2</strong>
<a href="javascript:setFocus(3);">3</a>
<a href="javascript:setFocus(4);">4</a>
</div></div>
<!--焦点图2结束-->
<!--焦点图3开始 标题13字 说明30个字-->
<div id="focusPic3" >
<a href="http://www..com/" class="i_photo_a" target="_blank">
<img src="images/03.jpg" /></a>
<h1><a href="http://www..com/" target="_blank">精致面容</a></h1>
<div id="index_page">
<a href="javascript:setFocus(1);">1</a>
<a href="javascript:setFocus(2);">2</a>
<strong>3</strong>
<a href="javascript:setFocus(4);">4</a>
</div></div>
<!--焦点图3结束-->
<!--焦点图4开始 标题13字 说明30个字-->
<div id="focusPic4" >
<a href="http://www..com/" class="i_photo_a" target="_blank">
<img src="images/04.jpg" /></a>
<h1><a href="http://www..com/" target="_blank">非入侵性除皱</a></h1>
<div id="index_page">
<a href="javascript:setFocus(1);">1</a>
<a href="javascript:setFocus(2);">2</a>
<a href="javascript:setFocus(3);">3</a>
<strong>4</strong>
</div></div>
<!--焦点图4结束--> </td>