Dear Sirs/Madam, We work on VB.NET,MS SQL & Crystal Report, We can make following process flow
-Sales Order,
-Pre Purchase order [To decide what to order against Sales order/to fullfill the requiremenet of Sales Order],
-Purchase order as decided from Pre-Purchase,
-Purchase according to Purchase order
-Proceess cycle[if you manufacture products]
-Sales [Invoices]
-Reports