1、先加入以下代码：
<script language="JavaScript" type="text/JavaScript">
<!--
function MM_preloadImages() { //v3.0
var d=document;
if(d.images)
{ if(!d.MM_p)
d.MM_p=new Array();
var i,j=d.MM_p.length,a=MM_preloadImages.arguments;
for(i=0; i<a.length; i++)
if (a[i].indexOf("#")!=0)
{ d.MM_p[j]=new Image;
d.MM_p[j++].src=a[i];
}
}
}
function MM_swapImgRestore() { //v3.0
var i,x,a=document.MM_sr;
for(i=0;a&&i<a.length&&(x=a[i])&&x.oSrc;i++) x.src=x.oSrc;
}
function MM_findObj(n, d) { //v4.01
var p,i,x;
if(!d) d=document;
if((p=n.indexOf("?"))>0&&parent.frames.length) {
d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
if(!(x=d[n])&&d.all)
x=d.all[n];
for (i=0;!x&&i<d.forms.length;i++)
x=d.forms[i][n];
for(i=0;!x&&d.layers&&i<d.layers.length;i++)
x=MM_findObj(n,d.layers[i].document);
if(!x && d.getElementById)
x=d.getElementById(n);
return x;
}
function MM_swapImage() { //v3.0
var i,j=0,x,a=MM_swapImage.arguments;
document.MM_sr=new Array;
for(i=0;i<(a.length-2);i+=3)
if ((x=MM_findObj(a[i]))!=null)
{document.MM_sr[j++]=x; if(!x.oSrc) x.oSrc=x.src; x.src=a[i+2];}
}
//-->
</script>
2、再在<body>中加入缓存图片：
onLoad="MM_preloadImages('images/menu_2a.gif')"
3、在要显示的格子中加入：
<a href="连接页面.asp" onMouseOut="MM_swapImgRestore()" onMouseOver="MM_swapImage('image2','','images/menu_2a.gif',1)"><img src="images/menu_2.gif" name="image2" border="0"></a>