<div id=Image1><a href="url1"><img src=image1.jpg></a></div>
<div id=Image2 style="visibility: hidden; position: absolute; left: -1000px; top: -1000px;"><a href="url2"><img src=image2.jpg></a></div>
<input type=button id=Button1 onclick="JavaScript: changeImage(1);">
<input type=button id=Button2 style="background-color: red;" onclick="JavaScript: changeImage(2);">
<script language="JavaScript">
function changeImage(n)
{
var div1 = document.getElementById("Image1");
var div2 = document.getElementById("Image1");
var btn1 = document.getElementById("Button1");
var btn2 = document.getElementById("Button2");
if(n == 1)
{
div1.style.visibility = "visible";
div1.style.position = "relative";
div1.style.top = div1.style.left = "";
div2.style.visibility = "hidden";
div2.style.position = "absolute";
div2.style.top = div1.style.left = "-1000px";
btn1.style.backgroundColor = "";
btn2.style.backgroundColor = "red";
}
else
{
div1.style.visibility = "hidden";
div1.style.position = "absolute";
div1.style.top = div1.style.left = "-1000px";
div2.style.visibility = "visible";
div2.style.position = "relative";
div2.style.top = div1.style.left = "";
btn1.style.backgroundColor = "red";
btn2.style.backgroundColor = "";
}
}
</script>