There is an update to ipsec-tools for CentOS 3.1
https://rhn.redhat.com/errata/RHSA-2004-165.html refers.
Updated files are :-
updates/i386/RPMS/ipsec-tools-0.2.5-0.4.i386.rpm updates/i386/SRPMS/ipsec-tools-0.2.5-0.4.src.rpm
which is also dependant on :-
updates/i386/RPMS/initscripts-7.31.13.EL-1.centos.1.i386.rpm updates/i386/SRPMS/initscripts-7.31.13.EL-1.centos.1.src.rpm
These are available at http://mirror.centos.org/3.1/ and should be on all mirrors within a few hours.
To update to the latest version 'yum update ipsec-tools' should be sufficient.
Lance