duplication of records

we have an glassware database( FM6 upgraded to FM8) that keep track of glassware produt in our storeroom. The database have fields like: Description, company,quantity, type of material( glass plastics, etc.) and now who own it. We need to keep track of who purchase what and how many of each item. All the info related to a purchased product will be the same as the remaining products in the storeroom ones except the quantity and new owner, it make sense to just duplicate the record and simply modify the new owner and quantity fields. We would like to automate this process and also prevent the purchase of more items than what we have in stock.

We are also accessing the database with the web (IWP).It's probably simple to do but I am not sure how to do it, any suggestion??