Filesystem monitoring question

[Cornelis Swanepoel]

I have a FreeBSD 6.0 box with a partition that is accessible to a number of
clients via SMB and NFS.

I would like to monitor activity on this partition so that every time a
write to it is completed, my C program is run (which stats the file and
stores some info about it in a database amongst other things)

My question is: What do I need to learn in order to construct a trigger for
my code?

If anyone can point me in the right direction I would greatly appreciate it.

Thanks

Cornelis