if (document.images) {
  image1on = new Image();
  image1on.src = "/images/clients/clients_img_btn1_on.gif";
  
  image2on = new Image();
  image2on.src = "/images/clients/clients_img_btn2_on.gif";
    
  image1off = new Image();
  image1off.src = "/images/clients/clients_img_btn1.gif";

  image2off = new Image();
  image2off.src = "/images/clients/clients_img_btn2.gif";
  
}

function changeImages() {
  if (document.images) {
    for (var i=0; i<changeImages.arguments.length; i+=2) {
      document[changeImages.arguments[i]].src = eval(changeImages.arguments[i+1] + ".src");
    }
  }
}