$(document).ready(function() { 
  $('input.submit').click(function() {
    var name = $('#name').val();    
    var email = $('#email').val();    
    var subject = $('#subject').val();    
    var message = $('#message').val();    

    if (!name) { $('#name').focus(); alert('Please enter a name'); return false; }
    if (!email) { $('#email').focus(); alert('Please enter an email'); return false; }
    if (!subject) { $('#subject').focus(); alert('Please enter a subject'); return false; }
    if (!message) { $('#message').focus(); alert('Please enter a message'); return false; }

    $('input.submit').val('Sending your message...').attr('disabled', true);

    $.post("/submit_contact.php", { name: name, email: email, message: message, subject: subject },
      function(data){
        $('input.submit').val('Your message has been sent');
      });
    return false;
  });
});