theAds = new Array();  

theAds[0] = "<a href=\"http://www.huajungroup.com/msr/\"><img src=images/680x62_topbanner11.jpg border=1></a>";  
theAds[1] = "<a href=\"http://www.myN5F.com/\"><img src=images/680x62_topbanner12.jpg border=1></a>"; 
theAds[2] = "<a href=\"http://www.huajungroup.com/msr/\"><img src=images/680x62_topbanner11.jpg border=1></a>";
theAds[3] = "<a href=\"http://www.TPY100.com/\"><img src=images/680x62_topbanner13.jpg border=1></a>";

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

while (rand >3) 
{    rand = Math.round(Math.random()*10); } 

document.write(theAds[rand]);