codice:
<body style="margin: 0px; padding: 0px; background: transparent url(bg-body2.png) no-repeat 50% 50%";
1. Manca la chiusura.

2. Meglio così:

La tua pagina
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="it">
<head>
<title></title>
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
<link rel="stylesheet" href="stile.css" type="text/css" />
</head>
<body>
</body>
</html>
Il tuo CSS esterno
codice:
body, html{
	margin: 0;
	padding: 0;
	width: 100%;
	height: 100%;
	background: url(bg-body2.png) center center no-repeat
}