You can enable SNMP, and use a snmp manager to receive traps, to collect all sorts of information... (including disk space, ...)
On most SNMP managers, you can launch actions when a certain trap or event is triggered.
(Action : sending an email, ...)
Before implementing snmp, please take a look around and learn some basic things about snmp :
communities (RO, RW, ...)
Which community strings to use or not to use and why,
...
Once implemented, you'll find it very very usefull
Good luck
Peter Peter Van Eeckhoutte
peter.ve@pandora.be