var menuImgExt = ".jpg";
var menuImgDir = "images/";

function menuPreload() {
	if (!document.images) return;
	for (var i = 0; i < document.images.length; i++) {
		if (new String(document.images[i].id).indexOf("menu_") == 0) {
			var img = new Image();
			img.src = menuImgDir + document.images[i].id + menuImgExt;
		}
	}
}

function menuSwap(name, onoff) {
	if (!document.images || !document.images[name]) return;
	
	var s = menuImgDir + name + (onoff ? "_sel" : "") + menuImgExt;
	document.images[name].src = s;	
}

function popup(f, w, h) {
	var x = (screen.width - w) / 2;
	var y = (screen.height - h) / 2;
	window.open(f, "popup", "width=" + w + ",height=" + h + ",left=" + x + ",top=" + y);
}