Table Automatically Populating with Data from another table

So I am working on this project, where I have an ITEM_PURCHASE table and an WAREHOUSE table I want users to be able to input data into the ITEM_PURCHASE table thru a form and the WAREHOUSE table will automatically populate from certain fields in ITEM_PURCHASE. In this scenario should I use a trigger or stored procedure? Can someone provide the SQL code to get me started? Can someone help me out here, it will be greatly appreciated.

Thanks

re: Table Automatically Populating with Data from another table

Trigger would be better for this one. Just use transactions to ensure consistency.

-- CK