A few years ago (ok a LOT) I had written a VERY simple network monitoring system for work. It primarily gathers syslog events, and does a basic TCP connect to check on machine state. This uses MSDE as it's engine for events.
Apache VirtualHost Transfer Counter is a set of files which allow you to quick and easy monitor utilization of http bandwitch on your server. It can give you also few statistics about VirtualHosts.