Along the way I found The Debian Universe, which "aims to become a complete guide to installing, managing and running Debian GNU/Linux." This is great because the last published book on Debian arrived in 2001 and described the 2.2r release.
I was able to update my kernel to 2.4.18 using the apt tools. This command showed me what was available:
apt-cache search kernel-image-2.4
Next I installed the 2.4.18 image:
apt-get install kernel-image-2.4.18-1-386
I added 'initrd=/initrd.img' to /etc/lilo.conf as prompted by the install process. When I rebooted I was running 2.4.18.
I intend to try upgrading to a 2.6 kernel using the packages provided by Debian Backports.