There is an updated ruby package for CentOS 3.3 (and added to 3.1)

https://rhn.redhat.com/errata/RHSA-2004-441.html refers

Updated files are :-

ruby-1.6.8-9.EL3.2.i386.rpm ruby-devel-1.6.8-9.EL3.2.i386.rpm ruby-libs-1.6.8-9.EL3.2.i386.rpm ruby-mode-1.6.8-9.EL3.2.i386.rpm

in updates/i386/RPMS/

in addition irb-1.6.8-9.EL3.2.i386.rpm has been added to the addons repository

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 run 'yum update'