function newImage(imgSrc) {
	var imgName = new Image();
	imgName.src = imgSrc;
	
	return imgName;
}
	
function changeImage(imgName, imgLocation) {
	document[imgName].src = imgLocation;
}
	
var preloadFlag = false;
function loadImages() {
	if (document.images) {
		index_on = newImage("asset/img/home-on.gif");
		index = newImage("asset/img/home.gif");
		catalogue_on = newImage("asset/img/catalogue-on.gif");
		catalogue = newImage("asset/img/catalogue.gif");
		purchase_on = newImage("asset/img/purchase-on.gif");
		purchase = newImage("asset/img/purchase.gif");
	
		preloadFlag = true;
	}
}