function banner() {
};

banner = new banner();
number = 0;

// bannerArray
banner[number++] = "<a href='http://tracker.tradedoubler.com/click?p=1231&a=925829&g=70508'><img src='http://impgb.tradedoubler.com/imp/img/70508/925829' border=0></a>"
banner[number++] = "<a href='http://tracker.tradedoubler.com/click?p=1231&a=925829&g=53346'><img src='http://impgb.tradedoubler.com/imp/img/53346/925829' border=0></a>"
banner[number++] = "<a href='http://tracker.tradedoubler.com/click?p=1231&a=925829&g=16535'><img src='http://impgb.tradedoubler.com/imp/img/16535/925829' border=0></a>"
banner[number++] = "<a href='http://tracker.tradedoubler.com/click?p=1231&a=925829&g=51724'><img src='http://impgb.tradedoubler.com/imp/img/51724/925829' border=0></a>"
banner[number++] = "<a href='http://tracker.tradedoubler.com/click?p=1231&a=925829&g=53345'><img src='http://impgb.tradedoubler.com/imp/img/53345/925829' border=0></a>"
// keep adding items here...

increment = Math.floor(Math.random() * number);

document.write(banner[increment])