gistfile1.php

//your modules config.xml in the event node
<sales_order_place_after>
    <observers>
        <customer_save>
            <class>sfintegration/observer</class>
            <method>salesOrderPlaceAfter</method>
        </customer_save>
    </observers>
</sales_order_place_after>



//..........    inside your model class (in this case {module path stuff}/Models/Observer.php)

/**
 * Collect order data and do stuff with it.
 *
 * @param Varien_Event_Observer $observer
 */
public function salesOrderPlaceAfter(Varien_Event_Observer $observer)
{
    
    /** @var $order Mage_Sales_Model_Order */
    $order = $observer->getOrder();

  //DO MORE STUFF HERE!
}