if (document.images) {

var btn1on = new Image();
btn1on.src = "../myimages/btn_us_on.gif";
var btn1off = new Image();
btn1off.src = "../myimages/btn_us_off.gif";



}

function On(name) {
  if (document.images) {
    document.images[name].src = eval(name + 'on.src');
  }
}

function Off(name) {
  if (document.images) {
    document.images[name].src = eval(name + 'off.src');
  }
}