Monitoring file usage and emailing based on changes

[David Haines]

I think that surely there must be a way to do this with Cron, but don't know
how to proceed exactly.

What I'm looking for is a way to monitor an FTP server (which is all it does
service-wise) running Mac OS X 10.2.8 (server) for changes to the users' FTP
directories, and sending an email (via sendmail) when a change has occurred,
and/or once per day, perhaps sending a notification (change=none, if nothing
has changed) ?

What would you do, have you done it, and how well is it working for you ?

TIA (!)