function hideLayer(whichLayer) {
if (document.getElementById) {
// this is the way the standards work
document.getElementById(whichLayer).style.visibility = "hidden";
}
else if (document.all) {
// this is the way old msie versions work
document.all[whichlayer].style.visibility = "hidden";
}
else if (document.layers) {
// this is the way nn4 works
document.layers[whichLayer].visibility = "hidden";
}
}

function showLayer(whichLayer) {
if (document.getElementById) {
// this is the way the standards work
document.getElementById(whichLayer).style.visibility = "visible";
document.getElementById(whichLayer).style.opacity = 100;
document.getElementById(whichLayer).style.filter  = "alpha(opacity=100)";
}
else if (document.all) {
// this is the way old msie versions work
document.all[whichlayer].style.visibility = "visible";
document.am.style.filter  = "alpha(opacity=100)";
}
else if (document.layers) {
// this is the way nn4 works
document.layers[whichLayer].visibility = "visible";
document.layers[whichLayer].style.opacity = "100";
}
}

function handleClick(whichClick) {

if (whichClick == "hide_am") {
hideLayer("am");
showLayer("am_link");
hideLayer("centerdiv");
}
else if (whichClick == "show_am") {
showLayer("am");
showLayer("centerdiv");
hideLayer("am_link");
}
}