The purchase order module under the contract module is really just a specialized type of contract for tracking at a summary level. If you are talking about procurement, you should take a look at the procurement module (Procurement ). This module comes with catalog workflows that integrate with the Product catalog and Stock rooms for sourcing and contains another purchase order table which is more full featured using line items as well as capabilities for receiving into the stock room. When talking about procurement this more likely what you are looking for.
This asset management video touches on some of the capabilities (Asset Management Tutorial - YouTube )
