Assuming buying more memory is out of the question there are many
things you can do to tighten up memory usage in Linux.
Many Linux distributions out of the box are quite bloated from a
memory perspective. They run more services and offer more features than most of
us will ever need. By removing many of these services you can free up several
megabytes of real memory.
My own system is a 486DX2-66 with 12MB of physical memory and 12MB
of swap space. It has run Linux for the last 3 years quite happily, and
hopefully it will run Linux for several more years. :)