I'm not sure of an easy way to distinguish which kernel comes with what update version. There may be a nice matrix somewhere with the information...
but here's the kernel number to update that are available in my RHEL4 install trees:
that is just the kernel version available with that particular release. You can be running an older kernel with every other package updated to the latest or any combination of package releases from general availability ( GA or "gold") to the latest.
you can also 'cat /etc/redhat-release' but this is just a reflection of what version of the 'redhat-release' rpm is installed.
another option may be to use 'lsb_release -a'
Hope this helps.