function banner(imgSource,chance) {
this.imgSource = imgSource;
this.chance = chance;
}
function dispBanner() {
with (this) document.write("<img src='" + imgSource + "' border=0 class=\"topimg\" />");
}
banner.prototype.dispBanner = dispBanner;
banners = new Array();
banners[0] = new banner("./img/top/img01.jpg",1);
banners[1] = new banner("./img/top/img02.jpg",1);
banners[2] = new banner("./img/top/img03.jpg",1);
banners[3] = new banner("./img/top/img04.jpg",1);
banners[4] = new banner("./img/top/img05.jpg",1);
banners[5] = new banner("./img/top/img06.jpg",1);
banners[6] = new banner("./img/top/img07.jpg",1);
banners[7] = new banner("./img/top/img08.jpg",1);
banners[8] = new banner("./img/top/img09.jpg",1);
banners[9] = new banner("./img/top/img10.jpg",1);
banners[10] = new banner("./img/top/img11.jpg",1);
banners[11] = new banner("./img/top/img12.jpg",1);


sum_of_all_chances = 0;
for (i = 0; i < banners.length; i++) {
sum_of_all_chances += banners[i].chance;
}
function randomBanner() {
chance_limit = 0;
randomly_selected_chance = Math.round((sum_of_all_chances - 1) * Math.random()) + 1;
for (i = 0; i < banners.length; i++) {
chance_limit += banners[i].chance;
if (randomly_selected_chance <= chance_limit) {
document.write("<img src='" + banners[i].imgSource + "' width=600 height=450 border=0 class=\"topimg\" />");
return banners[i];
break;
      }
   }
}