Hi Vitto, The tools you use depend massively on the kind of network you're building.
Things I'd look at would be RANCID, Cricket + genrtrconfig, Cacti, jffnms, mon from kernel.org, Nagios, ZenOSS, OpenNMS and my own NMS, Observer (http://www.observer.org).
You'll find lots of help with all of these tools from the mailling lists and forums related to them.
Good Luck! adam.
