ok.. id like to do this but i need some guide from you guys..

first is,
1. im thinking about creating a product, lets say a 3day subscription. so we have a product id.

i have also created a "Group dsicount" for 3 day in group pricing.

then my question:

a. where and what page can i "edit"? (write some code), that when a customer purchase this product (with the product id), it would change or alter the fields in customers table(in the discount pricing group field).
b. what would be the code to edit/add? (im not good in php)
c. any functions to be added? and what would it be?and where?


this is what i need as of now. ask later.

any help would great.

thanks