var rnd = Math.random() + '.' + (new Date()).getTime(); 
var banner = '<CENTER><A HREF="http://link.bannerlandia.com.ar/r/29674/1?1.3;468;60;' + rnd + '" TARGET="_top"><IMG WIDTH="468" HEIGHT="60" BORDER="0" ALT="Bannerlandia - Haz Click!" SRC="http://banners.bannerlandia.com.ar/s/29674/1?1.3;468;60;' + rnd + '"></A></CENTER>';

drew = new Array(2);
drew[0] ="A";
drew[1] ="B";
drew[2] ="B";
var idrew = drew[parseInt(Math.round(Math.random()*2))];

if (idrew == "A"){
document.write(banner);
}