var intBannerIndex = 1; //index of current banner
var t = setTimeout("ChangeAutoBanner()", 15000);//start to auto change of the banners in 15 sec

function ChangeBanner (prmBanner)
{
    clearTimeout(t);//stop the timeout
    $("#spnBanner" + intBannerIndex).hide(); //hide last banner
    $("#spnBanner" + prmBanner).show(); //show next banner
    intBannerIndex = prmBanner;//change banner index
    t = setTimeout("ChangeAutoBanner()", 15000); //call ChangeAutoBanner in 15 sec 
}

function ChangeAutoBanner()
{
    if (intBannerIndex != 4)//if not last banner
        ChangeBanner(intBannerIndex + 1);//change to next one
    else
        ChangeBanner(1);//change to first banner
}