Download the kernel-2.6.xx-x.*.src.rpm from http://ftp.redhat.com/pub/redhat/linux/enterprise/5Server/en/os/SRPMS/.

rpm -ivh kernel-2.6.xx-x.*.src.rpm

cd /usr/src/redhat/SPECS

rpmbuild -bb –target=i686 kernel-2.6.spec

cd /usr/src/redhat/RPMS

rpm -ivh kernel-2.6.xx-x.*.rpm