Magento - adding custom attribute to order

config.xml

<!-- 
add this to config.xml to have the attribute automatically
transferred to the order from the quote -> order conversion 

Access the attirbute via magic getters/setters
$quote->getYourSpecialAttribute()
$order->getYourSpecialAttribute()

$quote->setYourSpecialAttribute()
-->
<global>
...
    <fieldsets>
        <sales_convert_quote>
            <your_special_attribute>
                <to_order>*</to_order>
            </your_special_attribute>
        </sales_convert_quote>
    </fieldsets>
...
</global>

create_order_attribute.php

require_once('app/Mage.php');
Mage::app()->setCurrentStore(Mage::getModel('core/store')->load(Mage_Core_Model_App::ADMIN_STORE_ID));

$installer = new Mage_Sales_Model_Mysql4_Setup;
$attribute  = array(
   'type'          => 'int',
   'backend_type'  => 'text',
   'frontend_input' => 'text',
   'is_user_defined' => true,
   'label'         => 'My Label',
   'visible'       => true,
   'required'      => false,
   'user_defined'  => true,
   'searchable'    => true,
   'filterable'    => true,
   'comparable'    => true,
   'default'       => 0
);
$installer->addAttribute('order', 'special_attribute', $attribute);
$installer->endSetup();