asp.net application that manages an ftp server – Plesk

I have a requirement to build an application that a company can use to manage an ftp server. The idea is that through the web app, they can create users which will also create an ftp space etc so that the user can then upload documents and files to the company. The requirement is specifically that clients can use an ftp program and the company manages it through a web application.

I know Plesk provides an API which could be used by an asp.net application, as well as being able to work with IIS directly etc

however, can anyone suggest:
– a .net library that makes this straight forward (or just tell me that IIS is the best way to go)
– a package that does this (even if it costs)
– an alternate ftp server (not the IIS one) that may make this easier
– examples of .net code managing the IIS ftp server
– “just use plesk”! but really, plesk has too much in it, really I just want the ftp management part of plesk

assume it would be running on a windows server with complete control…I was just presuming that I’d interact with the IIS ftp server but cannot find any real examples of managing the ftp side of things (mind you, searching FTP IIS and .Net etc gives a real mixture of results)

thanks heaps!