I'm going to explain how I auto-start ratpoison on my bare-bones Debian Stable (Lenny) system. I don't use GDM, KDM, or any other "DM" (display manager). There are multiple steps here (involving multiple config files), but it is not complicated.
/etc/inittab & mingetty
mingetty is an alternative to getty, which (for the sake of simplicity) I describe as the linux login program. You'll need to install mingetty:
#as root (i.e., using either su or sudo)
apt-get install mingetty
The original plan
I've tried for a long time to have a usable, console-only, desktop linux system. By console-only, I mean running without X.org (a.k.a. X). I thought the key to this would be using the framebuffer. Here's wikipedia's definition of the framebuffer, but in short it allows displaying graphics without running X. When the framebuffer is enabled (some systems enable it by default), the first thing you notice is that the console font is smaller and nicer. This alone makes the console considerably more usable, as the screen doesn't scroll nearly as much, letting you see more at once. However, that's not all you can do with the framebuffer. You can also view PDFs, images, and video (using mplayer) with the framebuffer, and even compile complex programs to use the framebuffer instead of X (i.e. gimp, using GTK-DFB).
The main thing that stood in the way of my console-only desktop system is a modern browser. Now supposedly Firefox has been compiled for the framebuffer, as has uzbl. However, I've had no luck with either, and I've sunk a fair amount of time into the task. And links-g just doesn't cut it for me.