osc product attribute fix price to compute correctly

I need somebody good in osc to fix my osc install to compute correctly the automatic addition of an attribute price once a particualr product having that attribute is purchased. What you will do. 1. Customize the code so that when a customer purchase a minimum order of say, 15 items of product "A", he will automatically have to purchase product "C", and the price computed properly/correctly. Right now, I can't make it to work correctly.