Stumped by a version conflict.

Hi all...

I joined this list in an effort to solve a puzzle I fail to understand.
Thank you in advance for taking the time to read.

I've been managing a domain for the last eight years as an erstwhile
administrator. Erstwhile meaning it is largely a matter of setting up and
automating the routine functions of the machine. I am not by any stretch of
the imagination a guru. And please keep in mind that aside from minor tweaks
and upgrades, I pretty much leave the machine alone.

In that time, I've upgraded postgres 7.1 to 7.4 and now to 8.1 and have
rarely needed to reboot the machine. (Yay CentOS!) Manual installs from
source. Not RPM's

A few days ago however, the co-lo appears to have taken the system down for
a short time and brought it back up, essentially rebooting the system. No
big deal, except that until then, it had been running for almost two years.

Everything came back up as expected, with the exception of postgres. When I
went to start it manually, I got an error warning of an unrecognized
tcpip_socket parameter in postgresql.conf. Searching the 8.1 manual I
discovered it had been deprecated in favor of listen_addresses. Odd, but
okay.

I commented out the parameter (irrelevant since psql was configured with
defaults anyway) and tried starting it again. The next error I got was that
the database was initialized with version 7.4 and this version was 8.1.
What?

I checked the time stamps of the database I knew to be active, and yes,
there are several timestamps from two days ago so I kow that's the most
recent. PG_VERSION does indeed show 7.4 as the current version, and yet,
the binaries return 8.1.11 as the current version.

It should be noted at this point that medical problems have affected my
memory, so I may well be forgetting something obvious to the rest of you.
:)

So my questions are these: Since 8.1 binaries are the only ones that exist
on the machine, (in /usr/bin) how is it possible that they could have
utilized a database initialized with 7.4 in the first place? I thought
perhaps I started the server back then with an old binary, rather than
what's in the path, but I find no other instances of psql, pg_ctl, etc.
except whats in /bin/.

Without an answer to that, and since I can't start the server as it is
(apparently) currently compiled, I'd have to recompile 7.4, open the
database, dumpall with those binaries, initialize a new database with the
8.1 binaries, and restore the backed up db into the 8.1 structure. But if
the old 7.4 (current) db was running under 8.1 (and I still cant see how
that was possible) will it damage the db structure when it is restored?

Maybe the better question, though probably harder to answer is, "What am I
forgetting?"

Any thoughts or suggestions on how to restart postgres with the database I
know to be current will be especially helpful.

Thank you.