Scripting FTP usernames on win and nix server

I was wondering if anyone knew how to add users to an IIS FTP Server using a script like a batch file etc... and give each user his her own private dir on that FTP server. So if someone registers on my site my server side script executes this batch file with the users, username and password adding it to the FTP server and creating a dir with the same name as their username for ONLY them to access?

Also can IIS FTP usernames and passwords be added to an access database for IIS to read when a user authenticates, that would be the ideal solution if thats possible. Is it?

Also how do I do a similar thing on linux and what ftp servers are recommended for me to support?

I'm using PHP for this