As per the upstream vendors errata support policy, updates for CentOS 3 will also end on October 31th 2010. https://rhn.redhat.com/errata/RHSA-2010-0734.html
It is recommended that any system still running CentOS 3 should be upgraded to a more recent version of CentOS before this date to ensure continued security and bug fix support.
see also http://wiki.centos.org/HowTos/EOLC3
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