What are the basic programs needed to run XP

What are the basic programs needed to run XP Professional? I have come into possession of laptop that has an 80 Gig hardrive and I forget the Ram but it is large. The computer is full of junk and down to a few MB of hardrive left. As it is a nice laptop with large screen I thought I would keep for myself and would like to clean it to the basics and then put what I need on it for my business. So I would appreciate any information as to what I should keep so that it will still function correctly and delete the rest.