Purchase order form coding question

Hi,

How can I find code that's doing lookups and inserting values in fields based on entered ItemId on Purchase order form when a new line is entered? For example I'm interested in Unit price (PurchLine.PurchPrice) and Location (InventDim.wMSLocationId) fields. I'd like to also learn the logic and the structure that's used to perform these lookups, so I can quickly get to the code.