this depends on how you want to show admins and users they have uploaded files, and how you are saving the information on uploaded files.
Let's say for example, you are uploading images with captions... and you make a user upload form for the image and have a corresponding text field for the caption, you may save the information in a database such as mysql with the user's name, file id (auto generated), caption, image url in the database.
So when a user or admin logs in, you can access the database to recall files the user has uploaded. This is the more involved way to do so.
You can also do a user / pass combo to access a directory listing or simply do a directory browser yourself.
Each of these would serve your purpose, I think the DB however will give you most options.
