Showing message from php action script in form
<div id="register_user_box" class="inline_form" style="position: absolute; top: 20px; right: 10px; <br/>
     <span id="user_msg"></span><br/>
     <form action="register_user.php" method="post">
     <input type="hidden" name="id" id="id" value="add" />
     <input type="hidden" name="edit_user" id="edit_user" value="y" />
     <table cellspacing="0px"> <tr><td>Username:</td></tr><tr><td>
     <input type="text" name="uname" size="30" value="" class="inline_input"/></td> </tr> <tr><td>Email:</td></tr><tr><td>
     <input type="text" name="uemail" size="30" value="" class="inline_input"/></td> </tr> <tr><td>Password:</td></tr><tr><td>
     <input type="password" name="upass" size="30" class="inline_input"/></td> </tr> <tr><td>Confirm Password:</td></tr><tr> <td>
     <input type="password" name="cpass" size="30" class="inline_input"/></td></tr> </table></td></tr> </table> <p>
     <input class="button" type="submit" name="register" value="Register" style="float:right;"/></p>
     </form>
</div>

<?php

    $messages = array( 'usr_cred_req' => 'Must specify username, email, password.',
                        'usr_name_bad' => 'Bad username selection.  Select a different usrename.',
                        'usr_name_exists' => 'Username selected already exists.  Select a different username.',
                        'usr_email_bad' => 'Bad email selection.  Select a different email.',
                        'usr_email_exists' => 'Email selected already exists.  Select a different email.',
                        'usr_pass_notmached' => 'Passwords do not match.  Type passwords again.',
                        'usr_not_added' => 'User not added.',
                        'usr_not_updated' => 'User not updated.',
                        'usr_added' => 'User added.'
                        );

    $username = trim($_REQUEST['uname']);
    $email = trim($_REQUEST['uemail']);
    $password = md5(trim($_REQUEST['upass']));
    $copasswd = md5(trim($_REQUEST['cpass']));


    if ( $password != $copasswd ) { echo '<script> $("#usr_msg").html("'.$messages['usr_pass_notmached'].'"); </script>'; return;}
?>

if ( $password != $copasswd ) {
   $display_msg = $messages['usr_pass_notmached']
}

<span><?php echo $display_msg?></span>