1100000255 is order increment id not order id for system.
For getting order details by increment id ,You need to use
$order = Mage::getModel('sales/order')->loadbyIncrementId(1100000255);
loadByIncrementId() give single order not multiple Order
For Getting Orders of a particular Customer id then You should Call Sales order Collection
Mage::getModel('sales/order')->getCollection() Then filter that Collection id by field
That collection can be filter by any fields of sales_flat_order table,So as per as ,require you can get orders collection customer name, Customer email etc.