Excel to database

I have a problem I am not sure how to solve.
Basically its a invoicing system. I tried with all the products in the same excel file but then I realized if i update the product list it wont in all excel files for each customer. So i thought one external access database (or excel file) that I could refer to from an excel file.
So what I want to do now is when I want to add a new product to an invoice, I click a button (add) and it opens a small window with the list of products which has been taken from say an access database or excel file. Then I select the product and click insert.

How would I go about doing this? Are there any simple example I could follow?