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) {
		btn_archaeology_over = newImage("images/btn_archaeology_over.gif");
		btn_bombarding_over = newImage("images/btn_bombarding_over.jpg");
		btn_wallpaper_over = newImage("images/btn_wallpaper_over.gif");
		btn_harpsichord_over = newImage("images/btn_harpsichord_over.jpg");
		btn_jigsaw_over = newImage("images/btn_jigsaw_over.gif");
		btn_washington_over = newImage("images/btn_washington_over.jpg");
		btn_home_over = newImage("images/btn_home_over.jpg");
		preloadFlag = true;
	}
}