I use LinuxLinks and Distrowatch to compare various distros.
LinuxLinks has a good taxonomy, Distrowatch tells you what apps and versions are bundled in.
You might want to start with a
floppy-based distribution. I haven't seen them lately, but LOAF, FreeSCO, and Trinux all used to run on 16 MB machines. I still keep a Tom's Root & Boot floppy around, but it's mostly recovery oriented. You can also look at
mini-distros .