var rand3 = Math.random();
var rn3 = Math.floor(rand3*100+1);

<!-- Ultra Finishing ES Zanx.
if(rn3>=50 && rn3<=100) 
{
document.write('<a href="http://ad.zanox.com/ppc/?3485662C613114349T" target="_blank" rel="NoFollow"><img src="http://ad.zanox.com/ppv/?3485662C613114349" align="bottom" width="468" height="60" border="0" hspace="1" alt="Hudson Reed Cuartos de baņo"></a>');
}

<!-- Banner 468x60
if(rn3>=0 && rn3<50) 
{
document.write('<script src="http://www.gee.es/jscript/468x60.js" language="JavaScript"></script>');
}


<!-- Junkers
if(rn3>=-1 && rn3<-1) 
{
ord=Math.random();
ord=ord*10000000000000000000;
document.write('<SCR' + 'IPT LANGUAGE="JavaScript" SRC="http://ad.doubleclick.net/adj/N3710.ambienteyclima.com/B2162918;sz=468x60;ord='+ord+'?"><\/SCR' + 'IPT>');
document.write('<NOSCRIPT><A HREF="http://ad.doubleclick.net/jump/N3710.ambienteyclima.com/B2162918;sz=468x60;ord=123456789?" TARGET="_blank" rel="NoFollow"><IMG SRC="http://ad.doubleclick.net/ad/N3710.ambienteyclima.com/B2162918;sz=468x60;ord=123456789?" WIDTH="468" HEIGHT="60" BORDER="0" ALT=""></A></NOSCRIPT>');
}