When you say one category for each product, I am assuming you mean that although there may be multiple categories, each product would only be a member of one category? 
yes, that is what i mean.
if you are doing it this way, a product can onlt belong to one category, the create the category add / update pages
then on the product page, add a select list to select the associated category.
populate it from the category table using the category ID as the value.
in the product Insert / update behavior, bind the category column of the products table to the select list.
