Here's the first of hopefully several articles on Snort from our friends at CyberArmy:
This article will give you a brief overview of installing Snort on a Debian system. After reading this, you should have a basic setup logging daily to a local mailbox on your home linux system. In successive articles, I will delve further into the configuration of Snort as a Network Intrusion Detection System (NIDS).
Full story:
http://www.cyberarmy.net/library/article/1728/Don