Since I am running my Debian servers with a custom kernel I am constantly annoyed with messages asking me to also update the bundled 2.6.18 kernel in Debian Etch when running apt-get upgrade. This is why I came across these two commands that will stop apt-get to attempt to upgrade the kernel:

echo linux-image-2.6.18-6-686 hold | dpkg --set-selections
dpkg --get-selections linux-image-2.6-686

Replace linux-image-2.6.18-6-686 above with any package name to mark those packages as being held back.