in need of php code for user management/admin function...

hi... i'm looking for 'open source' code that can be used in a website for handling user registration, user admin functions... does anybody know of a good set of functions that can provide this kind of feature set. or, can anybody give me opinions regarding apps that you've used that have had this kind of functionality... as long as the code is open source, i can rip out/recode the functionality that i'm looking for... i'm looking for something that would be mysql based, with the ability to allow users to register/login, and have an admin function that allows the admin to deny/enable/disable users, as well as track various attributes within the site... if i have the basic shell/structure, i can modify the code to my needs.. comments/criticisms/thoughts... thanks bruce bedouglas@earthlink.net