Puppy Linux Distros Wiki

"Puppy Linux is a light-weight, yet fully featured, Linux distribution. It aims to be quick and useful on older machines, without sacrificing functionality. Puppy Linux is superior to other light-weight Linux distros because it has a lot of programs that haven't had featured lopped off to make them smaller.
Below are some graphical distros that are similar to Puppy in goals and design."

Under 25MB .. Under 50Mb .. Under 128Mb .. Under 256Mb .. Under 700Mb

http://puppylinux.org/wikka/Distros