Recently I’ve posted an article about the Windows manager and desktop environments that use less resources on Linux and thanks to a comment of Sebastian I’ve discovered Livarp, a lightweight GNU/Linux Distro.
Livarp is a DEBIAN-based distro that tries to take the best part of available Debian GNU/Linux applications without loosing accessibility or design, special attention was paid to the documentation that in a simple page collects all the most important information you need to know on the available software of this distribution and how to configure it.
And if this is not enough you can also visit the the irc freenode chan #livarp, where you can get more help for the installation/configuration.
Livarp can run on a PIII with 128M ram but is better with a PIV and 512M ram, higher configurations are just a bonus.