How to Linux network boot and install on PA-RISC - quick and dirty

I got a new HP 9000 C8000 workstation and it doesn't come with a CD drive or HP-UX preinstalled, and I don't want to get an optical drive in there just yet, so let's get it up and running with Linux network boot. It's much easier than it sounds. I'm using Gentoo but this would work for any Linux distribution on any platform, even standard PCs.