Well, first, I have to say I'm not an English speaker, so if I have any writting errors I'm sorry.
I'm developing a modification for an extension of a famous forum system. (It's simple , it's a forum).
I have got a form like this:

1.            <form method="POST" action="/mostrarPedido.php">
           <fieldset>
               <legend>Agregar Pedido</legend>
               <br />
               <strong>bbcode does not exist</strong>
               <br />            
               <textarea
                   style="width:95%;height:120px;"
                   id= "id_description"
                   onclick=""
                   name="pedido" id="id_description"></textarea><br />
               <input type="hidden" name="id_member" value="2">
               <input type="hidden" name="usuario" value="crazyfrog">
                   <strong>some stuff</strong>
               <br /><br />
               <input type="submit" value="Agregar Pedido" onclick="cargando(this.form.pedido.value,this.form.id_member.value,this.form.usuario.value);" id="submit_button"/><span id="cargando" style="display:none;"><img src="/images/ajax-loader.gif"> Cargando...</span>
           </fieldset>
           </form>
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

As you can see, there is a JavaScript event (onclick) on the <input> submit.
Into the event, there is a function (cargando) who needs the "pedido" value, "id_member" value and the "usuario" value.
This is the function:

1.  function cargando(pedido,id_member,usuario){
      $.ajax({
            type: "POST",
           url: "/mostrarPedido.php",
           data: "pedido="+encodeURIContent(pedido)+"&usuario="+encodeURIContent(usuario)+"&id_member="+id_member,
           success: function(h){
               $("#cargando").css("display","inline");
               $("#add_request").slideUp("fast");
               $("#ultimo_pedido").html(h);
               $("#ultimo_pedido").slideDown("slow");
           }
       });
    }
   
   
   
   
   
   
   
   
   
   
   
   

This is the mostrarPedido.php file:

1. <?php
   include('Settings.php');
   $con = mysql_connect($db_server, $db_user, $db_passwd);
   mysql_select_db($db_name,$con);
   include('SSI.php');
   global $context, $scripturl, $db_prefix;
   
   if($context['user']['id']=='')
   {
       echo'<span style="color: red;" class="size11"><b>Logueate rata...</b></span>';
   }
   else
   {
   $id_member = $_POST['id_member'];
   $usuario = $_POST['usuario'];
   $pedido = $_POST['pedido'];
   $fecha = date("l, j F Y");
   $fecha2 = date("g:i:s A");
   $fecha3 = $fecha . ' a las ' . $fecha2;
   
   mysql_query("INSERT INTO {$db_prefix}pedidos (ID_MEMBER, usuario, pedido, fecha) VALUES ('$id_member','$usuario','$pedido','$fecha3')");
   $query = mysql_query("SELECT ID FROM {$db_prefix}pedidos ORDER BY ID DESC");
   $obj = mysql_fetch_object($query);
   $last_id = $obj->ID;
   
   echo'
           <span id="',$last_id,'" style="display:block;">
           <strong>Por <a href="', $scripturl, '?action=profile;u=', $id_member, '">', $usuario, '</a> el ',$fecha, '.</strong>
           <br />
           <div style="font-size:11px; margin-top:5px;margin-bottom:5px;">
           ', $pedido, '
           </div>      
           <form method="post"><input size="5" maxlength="5" name="cerrar" />
           <input type="submit" value="Cerrar" name="enviar" /> <input type="hidden" name="request_id" value="', $last_id, '" />(Para cerrarlo ingresá el post ID)</form>
           <div style="border-bottom: 1px dotted #aaa; margin: 15px 35px 10px 0px;"></div>
           </span>';
   }
   ?>
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

I hope you understand, now the question is:
Can you tell me why when I click on the submit button does not load de Ajax?

If fact, I think I do all the things right, but the Ajax does not load, it shows the mostrarPedido.php, but not in the page I want to load it in. I'm new in jQuery .

Sorry for my English, thank you!