config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Ip_Test>
            <version>0.1.0</version>
        </Ip_Test>
    </modules>

    <global>
        <models>
            <test>
                <class>Ip_Test_Model</class>
            </test>
        </models>
        <events>
            <sales_order_place_before>
                <observers>
                    <auto_invoice_order>
                        <type>singleton</type>
                        <class>test/observer</class>
                        <method>implementOrderStatus</method>
                    </auto_invoice_order>
                </observers>
            </sales_order_place_before>
        </events>
    </global>

</config>

Observer.php

<?php

class Ip_Test_Model_Observer
{

    public function implementOrderStatus(Varien_Event_Observer $observer)
    {
        $order = $observer->getEvent()->getOrder();
        $orderItems = $order->getAllVisibleItems();
        foreach ($orderItems as $item) {
            $stockItem = Mage::getModel('cataloginventory/stock_item')->loadByProduct($item->getProductId());
            $stockItem->setQty(123456);
            $stockItem->save();
        }
    }

}