Its been a while since I did this and I'm not sure now how I managed to get it to work before.
What I have is a portal that is displaying line item fields. For the Product Name field, I have a drop down list that is related to the products table, to display the product names. So the user can click on which product they wish to choose to enter into the lineitem. What I am trying to do now is : once the user chooses a product name, to have filemaker pull other fields from the product record ex. unit cost, weight ect and show this information. This way, I can calculate total line item costs for each product.