if (document.images) {

button1first = new Image();
button1first.src = "../images/play1.gif";
button1second = new Image();
button1second.src = "../images/play2.gif";
button2first = new Image();
button2first.src = "../images/pause1.gif";
button2second = new Image();
button2second.src = "../images/pause2.gif";
button3first = new Image();
button3first.src = "../images/previous1.gif";
button3second = new Image();
button3second.src = "../images/previous2.gif";
button4first = new Image();
button4first.src = "../images/next1.gif";
button4second = new Image();
button4second.src = "../images/next2.gif";
}

function change_it(button)
{
 if (document.images)
 {
  document.images[button].src= eval(button+"second.src");
 }
}

function change_back(button)
{
 if (document.images)
 {
  document.images[button].src= eval(button+"first.src");
 }
}