<sales_order_save_before>
    <observers>
        <custom_observer>
            <type>singleton</type>
            <class>Custom_Module_Model_Observer</class>
            <method>updateaddress</method>
        </custom_observer>
    </observers>
</sales_order_save_before>

public function updateaddress(Varien_Event_Observer $observer) {
    $session = $observer->getEvent()->getCheckoutSession();
    $sessionCustomer = Mage::getSingleton("customer/session");
    $quote = $this->_quote = Mage::getModel('sales/quote')->setStoreId(Mage::app()->getStore()->getId())->load($session->getQuoteId());
    $address = $quote->getShippingAddress();
    if (!$sessionCustomer->isLoggedIn()) {
        $address->setData($reset);
        $quote->setShippingAddress($address);
        $quote->setBillingAddress($address);
        $quote->collectTotals()->save();
    }
}