The only IDS software that I'm familiar with is
, which is really powerful! You can install it over any linux or *BSD distribution, or even Windows (though that is not a very good idea). The very detailed
should cover you, at least for the initial steps of installation and configuration.
Keep in mind that Intrusion Detection/Prevention Systems can be as complicate as powerful you want them to be, so if you want to build something really good, you should be prepared to study quite a lot about related technologies and software. That said, the rabbit's hole gets really deep, but building a good and reliable IDS/IPS is a very intriguing and worthwile challenge! In any case keep us posted on your progress, ideas or problems -that's an interesting subject for discussion!