I have been playing with psad and fwsnort as a NIDS tool. They are light weight and very capable tools and I highly recommend both of them.
I was going to post a blog about these tools, but it kept growing longer and longer and involved init scripts, selinux policies, and apparmor profiles.
Rather then spamming the Ubuntu planet with all the details, I made a web page.
Sorry this blog is brief, but the above link will get you started using psad / fwsnort on Debian (squeeze) , Fedora 13 , or Ubuntu 10.04.
Feel free to post any feedback or comments here.
There is something wrong in your Howto:
Update psad signatures:
psad –sid-update
psad -H
Should be psad –sig-update.
Greetings
Seraphyn
Thank you Seraphyn, fixed that.