Installing IDS

Snort Rules
Without Proper Rules Snort is useless as an IDS.
There are 2 very good sources for snort rules.
www.snort.org has a great rule generator for your custom needs.
http://ids.whitehats.com/ids/ has a smaller but more up to the minute archive they try to update as soon as a new exploit comes out and they have detailed info on each of the exploits they have a rule for.

Snort Rules