Look for an older version of almost anything (Red Hat or Debian, perhaps) to run in 64Mb.

I did have Debian going in 48Mb once. Forget about Open Office with that little memory, but Abiword might be OK - again an older version will be smaller. Forget about compatibility with Office 97 - there's any Windows software that could do that in 64Mb either.

Finding a low-memory desktop and window manager is the key. There used to be lots, but now everybody's got enough memory to run the latest Gnome or KDE you'll have to dig a bit to find them. They are probably still available even on current distributions. Blackbox, for example, is in Debian Etch.

Anahata