FTP Server security

Hello.

I have an IIS 4 web server and I plan to create an FTP server on that machine in order to give to my users FTP access from outside to their personal folders.

Do you suggest any security measures that should I take into consideration before making this setup?

I.e. Shall I place a hard disk in another server and make it accessible through my IIS 4?

Any other suggestions to increase security? Could you tell me any web links that might help me?

Thank you in advance.