The following errata for CentOS-2 have been built and uploaded to the centos mirror:
RHSA-2009:0257-01 Critical: seamonkey security update
Files available: seamonkey-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-chat-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-devel-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-dom-inspector-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-js-debugger-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-mail-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-nspr-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-nspr-devel-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-nss-1.0.9-0.27.el2.c2.1.i386.rpm seamonkey-nss-devel-1.0.9-0.27.el2.c2.1.i386.rpm
More details are available from the RedHat web site at https://rhn.redhat.com/errata/rh21as-errata.html
The easy way to make sure you are up to date with all the latest patches is to run: # yum update