var nAds = 4;
var now = new Date()
var sec = now.getSeconds()
var ad = sec % nAds;
ad +=1;

if (ad==1) {
banner='<a href="http://ad.zanox.com/ppc/?6306046C691691244T"><img src="http://ad.zanox.com/ppv/?6306046C691691244" align="bottom" width="160" height="600" border="0" hspace="1" alt="hotel_160x600_20ko.gif"></a>';
}

if (ad==2) {
banner='<a href="http://ad.zanox.com/ppc/?13958297C31415536T"><img src="http://ad.zanox.com/ppv/?13958297C31415536" align="bottom" width="160" height="600" border="0" hspace="1" alt="Multi_160x600_20ko.gif"></a>';
}

if (ad==3) {
banner='<a href="http://ad.zanox.com/ppc/?13958311C1664530084T"><img src="http://ad.zanox.com/ppv/?13958311C1664530084" align="bottom" width="160" height="600" border="0" hspace="1" alt="promo3_160x600.gif"></a>';
}

if (ad==4) {
banner='<a href="http://ad.zanox.com/ppc/?13957959C585502460T"><img src="http://ad.zanox.com/ppv/?13957959C585502460" align="bottom" border="0" hspace="1" alt="Ski_160x600_2009"></a>';
}

document.write(banner);