Just adding a note that there are very capable and customizable packages like Nagios (formerly NetSaint), mon and Big Brother available freely to monitor just about everything you can think of in a network. I recommend you pick one of those instead of trying to roll your own - not only for reasons of robustness but also synergy. Any future improvements to them will benefit you automatically, and your own improvements to them will benefit many others as well.

Makeshifts last the longest.