Hi,
I think that you'll find your answer
there
:
You have two possibilities:
1. You can create a custom field of the table "order" via the menu Display->Custom fields. The field will appear during the checkout and attached to the order.
2. You can create a custom field of the table "item" via the menu Display->Custom fields. The field will appear on the product page and attached to the product in the cart (and later on to the product in the order).
In both cases, that is only possible with the Business edition. Also, in both cases, the information will be available in the emails and in the order details on the back end.
Hope this will help you.