var imagesupport = "false"

if (navigator.appName == "Netscape"){
        if (navigator.appVersion.substring(0,1) >= 3){
                imagesupport = "true";
                loadButtons();
        }
}

if (navigator.appName == "Microsoft Internet Explorer"){
        if (navigator.appVersion.substring(0,1) >= 4){
                imagesupport = "true";
                loadButtons();
        }

}

function loadButtons(){
   button = new Array(15);
   button_h = new Array(15);
   for (var i=1; i<40; i++)
   {
       button[i] = new Image();
       button[i].src = "img/boton" + (i) + "a.gif";
       button_h[i] = new Image();
       button_h[i].src = "img/boton" + (i) + "b.gif";
   }
}

function rollOver(oldbutton,newbutton){
        if (imagesupport == "true"){
                document.images[oldbutton].src=eval(newbutton + ".src");
        }
}