var banner = new Array(
'<a href="http://kf-forex.com.ua/bonuskf"><img src="http://forexnews.com.ua/images/cap_bonus_kf_c.jpg"></a>'

);

var banner_num = 0;
function banners(){
    if (banner_num < banner.length-1)
        banner_num ++;
        else
          banner_num=0;

    document.getElementById("cap_baner").innerHTML = banner[banner_num];
}

setInterval(banners,6000);