Upgrade to RedHat 9.0 broke PostgreSQL

I upgraded one of my RedHat machines from 8.0 to 9.0 and PostgreSQL
stopped working, with the following error message (reformatted here
for readability):

An old version of the database format was found.
You need to upgrade the data format before using PostgreSQL.
See (Your System's documentation
directory)/postgresql-7.3/README.rpm-dist for more information.

All I could find in that document which was relevant was:

These RPMs no longer support any sort of upgrading process other
than that documented in the regular documentation. That is, you
must dump, upgrade, initdb, and restore your data. The 7.2 to 7.3
migration can be quite difficult, even to the point of requiring
hand-editing of the dumpfile.

Thus, the 7.3 postgresql-server RPM specifically conflicts with
prior versions. The old server subpackage must be removed first,
the new package installed, and the data restored from dump.

Not the sort of thing I expected from an upgrade of the OS. So now
I'm faced with a Catch-22 dilemma: I need to dump the data with a
version of the database which is no longer on the machine.

I went back and pulled out my RedHat 8.0 CDs and tried to do a forced
downgrade of PostgreSQL to 7.2, but that failed because of dependency
conflicts.

So I pulled down the sources for 7.2.4, unpacked them, and ran
./configure and make. That failed, too, with the following errors:

...
gcc ... -o postgres
commands/SUBSYS.o(.text+0x41ce): In function `DoCopy':
: undefined reference to `errno'
commands/SUBSYS.o(.text+0x41d4): In function `DoCopy':
: undefined reference to `errno'
commands/SUBSYS.o(.text+0x42db): In function `DoCopy':
: undefined reference to `errno'
commands/SUBSYS.o(.text+0x42e1): In function `DoCopy':
: undefined reference to `errno'
collect2: ld returned 1 exit status

[... etc.]

So I'm stuck. Can I get two things, please?

1. A clue on how to get out of this box.

2. An explanation for why the box is necessary? I mean, it
would have been nice to have left behind sufficient tools
to do the dump PostgreSQL is requiring. If they were left
behind, it would have been nice if they were easier to find.

Apologies if this is in the FAQ -- I did look. I also looked at
http://www.postgresql.org/docs/view.php?version=7.3&idoc=1&file=admin.html
but the word "upgrade" doesn't appear anywhere in that detailed
table of contents.

Thanks in advance for any assistance.

Bob