var imagenumber=12;
var randomnumber=Math.random();
var banner1=Math.round((imagenumber-1)*randomnumber)+1;

images=new Array
images[1]="images/ads/ad_zgcb_ari.jpg"
images[2]="images/ads/ad_zgcb_tau.jpg"
images[3]="images/ads/ad_zgcb_can.jpg"
images[4]="images/ads/ad_zgcb_gem.jpg"
images[5]="images/ads/ad_zgcb_leo.jpg"
images[6]="images/ads/ad_zgcb_vir.jpg"
images[7]="images/ads/ad_zgcb_lib.jpg"
images[8]="images/ads/ad_zgcb_sco.jpg"
images[9]="images/ads/ad_zgcb_sag.jpg"
images[10]="images/ads/ad_zgcb_aqu.jpg"
images[11]="images/ads/ad_zgcb_cap.jpg"
images[12]="images/ads/ad_zgcb_pis.jpg"

var image=images[banner1]