New kernel packages are available for CentOS-3 x86_64. Please refer to https://rhn.redhat.com/errata/RHSA-2005-043.html:

RPMS/kernel-2.4.21-27.0.2.EL.ia32e.rpm
RPMS/kernel-2.4.21-27.0.2.EL.x86_64.rpm
RPMS/kernel-doc-2.4.21-27.0.2.EL.x86_64.rpm
RPMS/kernel-smp-2.4.21-27.0.2.EL.x86_64.rpm
RPMS/kernel-smp-unsupported-2.4.21-27.0.2.EL.x86_64.rpm
RPMS/kernel-source-2.4.21-27.0.2.EL.x86_64.rpm
RPMS/kernel-unsupported-2.4.21-27.0.2.EL.ia32e.rpm
RPMS/kernel-unsupported-2.4.21-27.0.2.EL.x86_64.rpm
SRPMS/kernel-2.4.21-27.0.2.EL.src.rpm