Does ipset work with the existing kernel under CentOS 5 and if so is there an RPM available? I've goggled around a bit, but haven't found anything. From http://ipset.netfilter.org/ I'm led to believe that the current kernel should support it.
Well, you have modules on your system, and if you Google you'll see a couple repos have the userland tools. Check out CentALT for example...