theAds = new Array();  

theAds[0] = "<a href=\"http://tech.sina.com.cn/\"><img src=../lib_barner/20020101_horse.gif border=1></a>";  
theAds[1] = "<a href=\"http://businessguide.zaobao.com/Singapore/psa/\"><img src=../lib_barner/20020105_sg_psa.gif border=1></a>"; 
theAds[2] = "<a href=\"http://www.legend.com.cn/\"><img src=../lib_barner/20020104_legend.gif border=1></a>";

var rand = Math.round(Math.random()*10); 

while (rand >2) 
{    rand = Math.round(Math.random()*10); } 

document.write(theAds[rand]);