var imgpath = "../logos/";

function showImage(imgName) {
  document.images["mainImg"].src = imgpath+imgName+".jpg";

  var elmt = document.sample_form.imgMenu;
  for (var i = 0; i < elmt.options.length; i++) {
    if (elmt.options[i].value == imgName) {
      elmt.selectedIndex = i;
      break;
    }
  }
}