function show_hide(oggetto){
	var obj = document.getElementById(oggetto);
	if ( obj != null ){
		var status = obj.style.display;
		if ( status == 'block' ){
			obj.style.display = 'none';
		}else{
			obj.style.display = 'block';
		}
	}
}

function open_window_credits() {
	window.open("credits.htm", null, "height=200,width=300,scrollbars=no,resizable=no,status=no,toolbar=no,menubar=no,location=no");
}

function roll(img_name, img_src){
   document.getElementById(img_name).src = img_src;
}