var how_many_ads = 2
var now = new Date() 
var sec = now.getSeconds() 
var ad = sec % how_many_ads; 
ad +=1; 
 
if (ad==1){
alt="ad1";  
banner="images/index_01.jpg"; 
width="343"; 
height="375"; 
} 

if (ad==2) {   
alt="ad2";  
banner="images/index_01_01.jpg";  
width="343"; 
height="375"; 
}
  
document.write('<center>'); 
document.write('<img src=\"' + banner + '\" width=') 
document.write(width + ' height=' + height + ' '); 
document.write('alt=\"' + alt + '\" border=0><br>'); 
document.write('</center>');