function tshirt_submit(){

  if ( $F('field_first_name') && $F('field_last_name')      && $F('field_street')   &&
       $F('field_city_town')  && $F('field_state_province') && $F('field_zip_code') &&
       $F('field_phone')      && $F('field_email')          && $F('field_tshirt') )
  {
    $('error_message').hide();
    $('form').submit();
  } else {
    $('error_message').show();
  }

}