Avevo saltato nel codice precedente l'id sul div, ecco il codice rivisto in base alla tua immagine:

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">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>La Mia Tesina</title>

<style type="text/css">
body {margin:0}
#container{
width:1050px;
height:660px;
position: relative;
margin:0 auto
}
img{
position: absolute;
top: 0;
left: 0;
z-index: 1;
border: 0;

}
iframe{
width: 756px;
height: 571px;
position: absolute;
top: 62px;
left: 246px;
z-index: 2;
border:0
}
</style>
</head>
<body>



<div id="container">
	[img]SFONDOTESINA.jpg[/img]
	<iframe src="pagina.html" name="riquadro" id="riquadro"></iframe>
</div>
<map name="Tesina" id="Tesina">
  <area shape="rect" coords="10,63, 159,86" href="ITALIANO.html" alt=" Italiano: Gabriele D'Annunzio"  target="riquadro" />
  <area shape="rect" coords="9,132, 134,154" href="STORIA.html" alt="..." target="riquadro" />
  <area shape="rect" coords="11,202, 140,220" href="DIRITTO.html" alt="..." target="riquadro" />
  <area shape="rect" coords="9,270, 154,291" href="SCIENZE.html" alt="..." target="riquadro" />
  <area shape="rect" coords="9,335, 191,361" href="ECONOMIA.html" alt="..." target="riquadro" />
  <area shape="rect" coords="10,400, 159,426" href="INGLESE.html" alt="..." target="riquadro" />
  <area shape="rect" coords="9,460, 234,497" href="INFORMATICA.html" alt="..." target="riquadro" />
  <area shape="rect" coords="8,533, 218,566" href="MATEMATICA.html" alt="..." target="riquadro" />
</map>


</body>
</html>
per avere una pagina caricata nell'iframe basta specificarla attraverso src