If you check the source (right click on the left frame) you will see they
used javascript, code below:
<html>
<head>
<script language="JavaScript">
<!--
if (document.images) {
image1on = new Image();
image1on.src = "people2.gif";
image1off = new Image();
image1off.src = "people.gif";
image2on = new Image();
image2on.src = "places2.gif";
image2off = new Image();
image2off.src = "places.gif";
image3on = new Image();
image3on.src = "wildlife2.gif";
image3off = new Image();
image3off.src = "wildlife.gif";
image4on = new Image();
image4on.src = "history2.gif";
image4off = new Image();
image4off.src = "history.gif";
image5on = new Image();
image5on.src = "facts2.gif";
image5off = new Image();
image5off.src = "facts.gif";
}
function changeImages() {
if (document.images) {
for (var i=0; i<changeImages.arguments.length; i+=2) {
document[changeImages.arguments].src =
eval(changeImages.arguments[i+1] + ".src");
}
}
}
// -->
</script>
<title>leftframe</title>
</head>
<body background="left.jpg">
<BR>
<a href="facts.html" style="cursor:help" target="mainFrame"
onMouseOver="changeImages('image5', 'image5on')"
onMouseOut="changeImages('image5', 'image5off')"><img name="image5"
src="facts.gif" alt="" border=0></a><BR><BR>
<a href="people.html" style="cursor:help" target="mainFrame"
onMouseOver="changeImages('image1', 'image1on')"
onMouseOut="changeImages('image1', 'image1off')"><img name="image1"
src="people.gif" alt="" border=0></a><BR><BR>
<a href="places.html" style="cursor:help" target="mainFrame"
onMouseOver="changeImages('image2', 'image2on')"
onMouseOut="changeImages('image2', 'image2off')"><img name="image2"
src="places.gif" alt="" border=0></a><BR><BR>
<a href="wildlife.html" style="cursor:help" target="mainFrame"
onMouseOver="changeImages('image3', 'image3on')"
onMouseOut="changeImages('image3', 'image3off')"><img name="image3"
src="wildlife.gif" alt="" border=0></a><BR><BR>
<a href="history.html" style="cursor:help" target="mainFrame"
onMouseOver="changeImages('image4', 'image4on')"
onMouseOut="changeImages('image4', 'image4off')"><img name="image4"
src="history.gif" alt="" border=0></a><BR><BR>
</body>
</html>
