Ti ringrazio linus ma ho risolto in con i while in questo modo:
$conn = mysql_connect($db_host,$db_user,$db_password) or die("Errore nella connessione a MySql: " . mysql_error());
mysql_select_db($db_database, $conn) or die("Errore nella connessione al database" . mysql_error());
$query = "SELECT uid FROM group_membership WHERE gid='6'";
$result = mysql_query($query, $conn) or die("nessun risultato" . mysql_error());
$tab.='<table width="100%" border="1">
<tr>
<td><div align="center">** Nominativo </div></td>
<td><div align="center"> Utenza </div></td>
<td><div align="center"> Indirizzo E-mail**</div></td>
<td><div align="center">** Assente **</div></td>
</tr>';
while ($ris = mysql_fetch_array($result)) {
$query1 = "SELECT uname, name, email FROM users WHERE uid='" . $ris['uid'] . "'" or die("Errore nella query " . mysql_error());
$result1 = mysql_query($query1,$conn) or die("nessun risultato" . mysql_error());
while ($ris1 = mysql_fetch_array($result1)) {
$Nominativo= $ris1['name'];
$Utenza= $ris1['uname'];
$Email= $ris1['email'];
$tab.='<tr>
<td><div align="center">'.$Nominativo.' </div></td>
<td><div align="center">'.$Utenza.' </div></td>
<td><div align="center">'.$Email.' </div></td>
<td><div align="center">** <input type="checkbox" name="select" value="selected"> **</div></td>
</tr>';
}
}
$tab.='</table>';
echo $tab;
?>