trying to find 6150 friendly OS download

We have an applemac 6150 that we used as
a server – hence
it lacks an operating system that would
make it useful for running quark on
(now we have a nice g4 server) I’m the
editor of a little free paper and I’m
losing the will to
live trying to find a free download of
the os that various IT-literate
friends claim you can get on the net,
but as we are a small group of papers
we have no specific IT man so it is down
to me.
Can yo