Re: 8.0 installs ok, but then...

Thanks for the response.
First, more background:
 - running on win xp
 - my pc is the only one with this problem in a group of about 20 upgrades
 - made sure there's nothing in my PATH that would cause this problem
 - found a workaround: changed "md5" to "trust" in pg_hba.conf

    > ...every psql command I issue gets this response:
    > psql: FATAL:  password authentication failed for user "postgres" even
    > though there is no password prompt.

    What shows up in the postmaster log?

I can't find a postmaster log. Didn't know what one was til your question prompted me to find out, and I'm having
troublemapping the doc's unix examples to my win environment. As far as I can figure, the postmaster task on my pc is
thePostgreSQL Database Server 8.0 service. And I haven't figured out yet where the log is for that. 
Here's the content of C:\Program Files\PostgreSQL\8.0\data\pg_log\postgresql-2005-03-23_000000.log:

2005-03-23 11:03:29 FATAL:  password authentication failed for user "jon.allen"
2005-03-23 11:05:08 FATAL:  password authentication failed for user "postgres"
2005-03-23 11:24:05 FATAL:  password authentication failed for user "postgres"
2005-03-23 13:36:41 FATAL:  password authentication failed for user "jon.allen"
2005-03-23 13:36:48 FATAL:  password authentication failed for user "jon.allen"
2005-03-23 13:36:52 FATAL:  password authentication failed for user "jon.allen"
2005-03-23 13:36:54 FATAL:  password authentication failed for user "jon.allen"
2005-03-23 15:07:02 LOG:  received fast shutdown request
2005-03-23 15:07:02 LOG:  shutting down
2005-03-23 15:07:02 LOG:  database system is shut down
2005-03-23 15:07:03 LOG:  logger shutting down

    > I don't have any .pgpass files on my system.

    How about PGPASSWORD environment variable?

No postgres-related environment variables.

    > The install log mentions errors 1707 and 1709, but I can't find any
    > reference to them.

    Actually showing them to us might help...

The last 12 lines from the install log (let me know if you need to see the whole 3 Mb):

=== Logging stopped: 3/22/2005  15:47:39 ===
MSI (c) (14:60): Note: 1: 1707
MSI (c) (14:60): Note: 1: 2205 2:  3: Error
MSI (c) (14:60): Note: 1: 2228 2:  3: Error 4: SELECT `Message` FROM `Error` WHERE `Error` = 1707
MSI (c) (14:60): Note: 1: 2205 2:  3: Error
MSI (c) (14:60): Note: 1: 2228 2:  3: Error 4: SELECT `Message` FROM `Error` WHERE `Error` = 1709
MSI (c) (14:60): Product: PostgreSQL 8.0 -- Installation completed successfully.

MSI (c) (14:60): Grabbed execution mutex.
MSI (c) (14:60): Cleaning up uninstalled install packages, if any exist
MSI (c) (14:60): MainEngineThread is returning 0
=== Verbose logging stopped: 3/22/2005  15:47:40 ===