Point of Sale System database

I am using VB Express 2008 and MsAccess as Database. I am trying to develop a Poit of sale system for a restaurant. I have done the basic work with Vb. Now i am having problems with MsAccess to record the Inventory system. Like the stock is updated with the sale of items and to have reports of updated stock at any time. Can you help me with some ideas to create and maintain inventory system linked to the Point of Sale system. Thanks