function img_on(imgName) {
  if (document.layers){
    imgOn = eval(imgName + "_on.src");
    document.layer.document [imgName].src = imgOn;
  }
  else if( document.all ){
    imgOn = eval(imgName + "_on.src");
    document [imgName].src = imgOn;
  }
  else {
    imgOn = eval(imgName + "_on.src");
    document [imgName].src = imgOn;
  }
}

function img_off(imgName) {
  if (document.layers){
    imgOff = eval(imgName + "_off.src");
    document.layer.document [imgName].src = imgOff;
  }
  else if( document.all ){
    imgOff = eval(imgName + "_off.src");
    document [imgName].src = imgOff;
  }
  else {
    imgOff = eval(imgName + "_off.src");
    document [imgName].src = imgOff;
  }
}

function img_act(imgName) {
  img_on(imgName);
}

function img_inact(imgName) {
  img_off(imgName);
}