Ti ringrazio per la risposgta ma non funziona, ti rimetto il codice css
Codice PHP:
body{
margin: 0; 
padding: 0;
text-align: center;
background-color: #333;
padding-top: 20px;
} 
 html, body { width: 100%; } 
 #centralone_home {
width: 640px;
height: 625px;
margin: auto;
background: url("../images/home.png")no-repeat;  }
#centralone_abbonati {
width: 640px;
height: 625px;
margin: auto;
background: url("../images/abbonati.png")no-repeat;  }
#sponsor {
float: right;
width: 175px;
height: 120px;
background-color: white; } 
e il codice nella pagina
Codice PHP:
<!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">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>StupendoMag</title>
<link rel="stylesheet" type="text/css" href="css/stile.css" />
</head>
<body>
<div id="centralone_home">
<div id="prima_parte_home"></div>
</div>
<div id="sponsor"></div>
</body>
</html>