come non detto....mi mancava l'action del form....ora va
Codice PHP:
function openPopUp(){
    
window.open('','miaPop');
}

<
FORM action="quickActive.php" method="post" target="miaPop" onsubmit="openPopUp();"
<
input  type="text" name="user" size="12" value="login" >
 
<
input type="password" name="password" size="12">
 
<
input type="submit" name="check" value="entra"
</
FORM