How to track query execution time

I've got a web site (apache/php) with a postgres 8.2.5 database(s).

We're now getting some periods of high load.  We have a lot of dynamic
queries so I'm not able to just tune and optimize a few known queries
ahead of time.

Is there a way that I can get a list of all the actually SQL queries
as passed to Postgres and the start/completed times (or even just
duration)?
This doesn't need to be real time, log parsing after the fact would
probably be fine too.

Then, I could look at the worst performers and figure out where in the
PHP code that query was built from and then try to tune from there.

Thanks.