admin site ajax plugin

hi i have some error for my first wordpress plugin

i make the plugin admin site juqery and ajax to update database
but it not work. can somebody give some advice.

below is the code

index.php

// Hook for adding admin menus
add_action('admin_menu', 'dinar_currency_pages',5);

// action function for above hook
function dinar_currency_pages() {
    // Add a new top-level menu
	//add_menu_page( $page_title, $menu_title, $capability, $menu_slug, $function, $icon_url, $position );
    add_menu_page('Dinar Currency', 'Dinar Currency', 'manage_options', 'currency', 'currency_admin' );
}

// Currency Page
function currency_admin() {

	global $wpdb;
	$table_name = $wpdb->prefix . "dinar";

	$plugin_url=WP_PLUGIN_URL;

	global $current_user;

	//get_currentuserinfo();
	$user = $current_user->user_login;

	$datetime = gmdate("Y-m-d H:i:s ");

	$query = mysql_query("SELECT id, currency, disc, thumb FROM wp_dinar");

	echo "
	<form method='post' action='update.php'>
	<div id='container'>
	<div id='main'>
	";

	echo "<ul id='photos'> \n";

	while( $row = mysql_fetch_assoc($query)){

		$currency = $row['currency'];
		$thumb = $row['thumb'];
		$id = $row['id'];

		echo "<li><img src='images/$thumb' id='$id' width='160' height='120'/>\n";
		echo "<h4>$currency</h4> \n";
		echo "<input type='text' name='currency' value='$currency' /></li> \n \n";
		}	

		echo "</ul>";

		echo "

			<div id='response' class='hidden' />
	</div><!-- end main-->

</div><!-- end container-->
</form>

		";

}

add_action( 'admin_print_styles', 'admin_enqueue_styles' );

function admin_enqueue_styles() {

	wp_enqueue_style( 'admin', ex_plugin_url( 'css/style.css' ),
		array(), EXCHANGE_VERSION, 'all');

	wp_enqueue_script( 'myscript', ex_plugin_url( '/script.js' ), EXCHANGE_VERSION);
	wp_deregister_script( 'jquery' );
    wp_register_script( 'jquery', 'http://ajax.googleapis.com/ajax/libs/jquery/1.5/jquery.min.js','v1.51');
    wp_enqueue_script( 'jquery' );
}

script.js

$(function() {
    $('form').attr('action', '');

    $('h4').click(function() {

        $(this).slideUp().next('input').slideDown();
    });

    $('ul#photos input').change(function() {
        var id = $(this).parent('li').find('img').attr('id');
        var thisParam = $(this);
        var currency = $(this).val();

        $.ajax({
            type: 'post',
            url: 'update.php',
            data: 'currency=' + currency + '&id=' + id,

            success: function(response) {
                $('input').slideUp();
                $(thisParam).prev('h4').text(currency).slideDown();

                $('#response').fadeIn('1000').empty().append(response).prepend('<span id="x">X</span>');

                $('span#x').click(function() {
                    $('div#response').fadeOut('slow');
                });

            }

        });

    });
});

update.php

global $wpdb;
$table_name = $wpdb->prefix . "dinar";

$currency = $_POST['currency'];
$id = $_POST['id'];

//$query = mysql_query("SELECT id, title, src FROM photos");
$update_query = mysql_query("UPDATE wp_dinar SET currency = '$currency' WHERE id='$id'");

//$result = $mysqli->query($update_query) or die(mysqli_error($mysqli));

//if ($result) {
	echo "Success! <br />";
	echo "The title of this photo has been changed to:  <strong>$title</strong>";
//}