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) {
		gaiyo_over = newImage("contents/gaiyo-over.gif");
		bunseki_over = newImage("contents/bunseki-over.gif");
		setsubi_over = newImage("contents/setsubi-over.gif");
		shizai_over = newImage("contents/shizai-over.gif");
		bosyu_over = newImage("contents/bosyu-over.gif");
		link_over = newImage("contents/link-over.gif");
		sitemap_over = newImage("contents/sitemap-over.gif");
		preloadFlag = true;
	}
}