I just set up a Windows 2003 Primary Domain Controller with Core FTP Server and I am really very impressed.
I also have iis 6.0 running. I have stopped the IIS FTP service and replaced it with Core FTP Server.
Not only did I get it running in a short time, I even got SFTP running and did not have to punch any holes in my firewall. I only have port 22 forwarded from the router and through the firewall and it WORKS..
Even running standard FTP on port 21, only had 21 forwarded and it works passive over the internet without ANY other ports opened (and not defining and ports in Core FTP server as well!
I had been having issues with IIS 6.0 and Routing and Remote access, with NAT. Apparently there is some issue there, and despite a hotfix it still was not working on file tanafers (they stop about 98%).
I then got a trial version of ws_ftp server (sorry to mention a competitor), but I had to hammer open so many ports for passive to work (cant use active as I am on a symetrical multiple WAN IP via a gateway IP).
I then got Core FTP server and had it running without hammering my firewall to bits. I was so impressed less than a day into it I purchased a license.
Wonderful piece of software.
Cheers,
David