FireFore

var how_many_ads = 3;  
var now = new Date()  
var sec = now.getSeconds()  
var ad = sec % how_many_ads;  
ad +=1;  
if (ad==1) {   
url="http://passport.panda.org/index.cfm";  
alt="加入WWF“熊猫护照”的行列，支持中国大熊猫保护事业！";  
banner="http://www.i0595.net/images/i0595_panda.org.gif";  
width="468";  
height="60";  
}  
if (ad==2) {   
url="http://angel.crcf.org.cn/";  
alt="中国红十字基金会“救救白血病孩子！”";  
banner="http://angel.crcf.org.cn/images/aixin1.gif";  
width="468";  
height="60";  
}  
if (ad==3) {   
url="http://www.conservation.org.cn/pledge/index.htm";  
alt="保护国际-绿色旅游公益活动！”";  
banner="http://www.conservation.org.cn/pledge/img/Banner470X60.jpg";  
width="468";  
height="60";  
}     
document.write('<a href="' + url + '" target="_blank">');  
document.write('<img src="' + banner + '" width=')  
document.write(width + ' height=' + height + ' ');  
document.write('alt="' + alt + '" border=0>');

<script language="javascript" type="text/javascript" src="banner.js"></script>