function newImage(arg) {
	if (document.images) {
		rslt = new Image();
		rslt.src = arg;
		return rslt;
	}
}

function changeImages() {
	if (document.images && (preloadFlag == true)) {
		for (var i=0; i<changeImages.arguments.length; i+=2) {
			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
		}
	}
}

var preloadFlag = false;
function preloadImages() {
	if (document.images) {
		zbuilding_over = newImage("imgs/zbuilding-over.jpg");
		zfood_over = newImage("imgs/zfood-over.jpg");
		zlandscape_over = newImage("imgs/zlandscape-over.jpg");
		zportrait_over = newImage("imgs/zportrait-over.jpg");
		zvarious_over = newImage("imgs/zvarious-over.jpg");
		znight_over = newImage("imgs/znight-over.gif");
		preloadFlag = true;
		changeImages('zbuilding', 'imgs/zbuilding.jpg'); 
		changeImages('zfood', 'imgs/zfood.jpg'); 
		changeImages('zlandscape', 'imgs/zlandscape.jpg'); 
		changeImages('zportrait', 'imgs/zportrait.jpg'); 
		changeImages('zvarious', 'imgs/zvarious.jpg'); 
		changeImages('znight', 'imgs/znight.gif'); 
	}
}