Internet File Sharing System

I wish to create a secure file-sharing system to run on a server (Linux or Windows) which will allow me to provide file-sharing services to Windows users over the Internet by mounting a virtual drive on the users' PC. Users could upload and download files to and from the virtual drive, etc. I would need the ability to specify which users can access which virtual directories on the server. I'm aware that these features are most likely readily available using existing applications (Windows Server, Samba, etc.) but I need someone to basically set things up so I can administrate it.