In around 2002, I got my hands on an old 386 which I was planning to use for teaching myself things. I was able to breathe life into it using MicroLinux. Two superformatted 1.44" floppy disks and the thing booted. Basic kernel, 16 colour X display, C compiler and Editor.

I don't know if there are any other options for older machines other than stripped down Linux distros.