A corefile is of no value to anyone running on a platform even slightly
different from your own. Could you please compile psql with -g,
reproduce the problem, and then send in a gdb backtrace from that core?
Also, what exactly are you doing that provokes the coredump?
FWIW, I have a RedHat 5.1 box on which I sometimes test postgres,
so the mere fact that your system is old isn't the issue.
regards, tom lane