Wow, and I thought I was 'pushing it' by installing Linux on a 400Mhz K6-2 with 256 MB of RAM...
You seem to have already discovered the smallest and lightest distros available. The main reason for the increasing system requirements of
all OSes is the fancy graphical interfaces, btw, so consider if you can't do what you need/want to do running in command line ("text") mode. There is a browser called Lynx that runs without a graphical desktop. Plenty of text mode editors are available for Linux, too.