whaton = new Image();
whatoff = new Image();
whatactive = new Image();
materialson = new Image();
materialsoff = new Image();
materialsactive = new Image();
howon = new Image();
howoff = new Image();
howactive = new Image();
whyon = new Image();
whyoff = new Image();
whyactive = new Image();
printon = new Image();
printoff = new Image();

whaton.src = "images/what_roll.gif";
whatoff.src = "images/what.gif";
whatactive.src = "images/what_active.gif";
materialson.src = "images/materials_roll.gif";
materialsoff.src = "images/materials.gif";
materialsactive.src = "images/materials_active.gif";
howon.src = "images/how_roll.gif";
howoff.src = "images/how.gif";
howactive.src = "images/how_active.gif";
whyon.src = "images/why_roll.gif";
whyoff.src = "images/why.gif";
whyactive.src = "images/why_active.gif";
printon.src = "images/printableversion_roll.gif";
printoff.src = "images/printableversion.gif";

var layerRef = "";
var styleRef = "";
var oldLayer = "layerwhat";
var currentbutton = "what";

var agt=navigator.userAgent.toLowerCase();
var is_nav  = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('spoofer')==-1) 
				&& (agt.indexOf('compatible') == -1) && (agt.indexOf('opera')==-1)
				&& (agt.indexOf('Webtv')==-1) && (agt.indexOf('hotjava')==-1));
var is_major = parseInt(navigator.appVersion);
var is_nav6up = (is_nav && (is_major >= 5));

if (navigator.appName == "Netscape") {	
     layerRef = ".layers";
     styleRef = "";
}
else {
     layerRef = ".all";
     styleRef = ".style";
}

function mouseOverButton(button){

	if(button != currentbutton){
		swap(button, button + "on", null);
	}
}

function mouseOutButton(button){

	if(button != currentbutton){
		swap(button, button + "off", null);
	}

}

function clickButton(button){

	if(button == currentbutton) return;
	
	swap(currentbutton, currentbutton + "off", null);
	swap(button, button + "active", null);
	currentbutton = button;
	clickLayer("layer" + button);

}

function clickLayer(layerName){

     if(oldLayer){
     	if(oldLayer == layerName) return;
     	else hideLayer(oldLayer);
     }
     if(is_nav6up){
     	document.getElementById(layerName).style.visibility = "visible";
     }
     else{
     	eval( "document" + layerRef + "[layerName]" + styleRef + ".visibility = 'visible'"); 	
     }
     oldLayer = layerName;
}


function hideLayer(layerName) {

	if(is_nav6up){
		document.getElementById(layerName).style.visibility = "hidden";
	}
	else{
		eval( "document" + layerRef + "[layerName]" + styleRef + ".visibility = 'hidden'");
	}
}

function swap(image_name,new_source,div) {
	if (document.images) {
		if (document.layers && div!=null) eval('document.'+div+'.document.images["'+image_name+'"].src = '+new_source+'.src');
		else document.images[image_name].src = eval(new_source+".src");
	}
}