Magento 1.8 – How to Get Last OrderId Inside an Observer

I am trying to get the last order id for an order so that I can create an invoice and shipment automatically but I can't seems to load the correct orderId to perform the action…

Here is how I am trying to load the orderId Observer.php

$order = Mage::getModel('sales/order')->load($orderid);
$orderIncrementId = $order->getIncrementId();

If the orderId is not present throw exception

$order = Mage::getModel('sales/order')
            ->loadByIncrementId($orderIncrementId);    
if (!$order->getId()) {
        Mage::throwException("Order does not exist, for the Shipment process to complete");
    }

The problem is if I pass in a static orderId no exception is thrown

$orderIncrementId = '1100000023-4';

But when I try to load it through the Model I can't

Can anyone show me how to get the orderId for an order please?