help with php/mysql logic for music stat site

i found an open source php script that will take a user's exported itunes xml file and import the songs, artists, albums, and play counts into a database. i edited this so that anyone can upload their library file and import their data. it's all in one big database.

i'm wondering, could anyone help me with adding users to this? like the ability to have a stats page and everything for each user. and also some sort of friendship-like functionality to compare music tastes, etc. the problem is getting the logic started on how go about in the database for adding the users, and how to separate them.

thanks