browserName = navigator.appName; 
browserVer = parseInt(navigator.appVersion);
if (browserName == "Netscape" && browserVer >= 3){
  init = "net";
  }
  else{
  init = "ie";
  }

if ((init == "net")||((init == "ie")&&(browserVer >= 4))){
  image_nor_on = new Image();
  image_nor_on.src = "/images/home/bot-enviar-on.gif";
  image_nor_off = new Image();
  image_nor_off.src = "/images/home/bot-enviar-off.gif";

  image_use_on = new Image();
  image_use_on.src = "/images/home/bot-usuarios.gif";
  image_use_off = new Image();
  image_use_off.src = "/images/home/bot-enviar-off.gif";

  image_pre_on = new Image();
  image_pre_on.src = "/images/home/bot-premium.gif";
  image_pre_off = new Image();
  image_pre_off.src = "/images/home/bot-enviar-off.gif";

}

function boton_on(imgName)
    {
    if (((init == "net")&&(browserVer >=3))||((init == "ie")&&(browserVer >= 4))){
    imgOn = eval(imgName + "on.src");
    document[imgName].src = imgOn;
    }
    }

function boton_off(imgName)
    {
    if (((init == "net")&&(browserVer >=3))||((init == "ie")&&(browserVer >= 4))){
    imgOff = eval(imgName + "off.src");
    document[imgName].src = imgOff;
    }
}