<!-- Home -->

if (document.images) {

  var button1_up = new Image();
  button1_up.src = "images/navigation/home_off.jpg";
  
  var button1_over = new Image();
  button1_over.src = "images/navigation/home_on.jpg";
}

function over_button1() {
  if (document.images) {
    document["buttonOne"].src = button1_over.src
  }
}

function up_button1() {
  if (document.images) {
    document["buttonOne"].src = button1_up.src
  }
}

<!-- Save -->

if (document.images) {

  var button1_up2 = new Image();
  button1_up2.src = "images/navigation/save_off.jpg";
  
  var button1_over2 = new Image();
  button1_over2.src = "images/navigation/save_on.jpg";
}

function over_button2() {
  if (document.images) {
    document["buttonTwo"].src = button1_over2.src
  }
}

function up_button2() {
  if (document.images) {
    document["buttonTwo"].src = button1_up2.src
  }
}

<!-- Contact -->

if (document.images) {

  var button1_up3 = new Image();
  button1_up3.src = "images/navigation/contact_off.jpg";
  
  var button1_over3 = new Image();
  button1_over3.src = "images/navigation/contact_on.jpg";
}

function over_button3() {
  if (document.images) {
    document["buttonThree"].src = button1_over3.src
  }
}

function up_button3() {
  if (document.images) {
    document["buttonThree"].src = button1_up3.src
  }
}