pg_log - automatic logging of every transaction? how to access?

I'm trying to figure out if postgres logs every transaction somewhere, and if
so, how to access that.

From my own exploring, as well as reading the archives of the pgsql-novice,
pgsql-general, and pgsql-questions mailing lists, I'm assuming that this is
the purpose of pg_log (and/or pg_time?).

I see that the modification times of those files are updated whenever I
perform an SQL query, but I can't directly access them:

lounge=> select * from pg_log;
WARN:pg_log cannot be accessed by users
lounge=> select * from pg_time;
WARN:pg_time cannot be accessed by users

Is this the purpose of these files, and if so, how do I get at them?

Or if I want to keep track of certain transactions, do I have to create a log
relation within the database and update it with transactions that I care
about?  (Which seems like a hack that I'm assuming is unnecessary.)

Numerous people have asked questions about this in the past, but I have not
been able to find a single response.  The only responses had to do with a (now
fixed) postgres bug that caused pg_time and pg_log to grow unnecessarily large.

- Rich Fromm
rfromm@cs.berkeley.edu

p.s. Apologies in advance for cross-posting to pgsql-novice and pgsql-general;
I wasn't sure which was more appropriate.