Storage location of temporary files

Hi list,
I want to optimize the performance of our PostgreSQL 8.2 server. Up to
now the server has a raid1 where the whole database is located
(including tha WAL files). We will now move the database to a raid5
(which should be faster than the raid1) and will also move the WAL to a
separate disk (which should, according to the docs, also increase the
performance).
But I see the temporary files as another important performance
bottleneck. From the docs (chapter 17.4.1):

work_mem (integer)
Specifies the amount of memory to be used by internal sort
operations and hash tables before switching to temporary disk files.
[...]

We have rather complex queries and as I far as I see from the disk usage
patterns the system makes use of temporary disk files. So I would like
to use a faster disk for these temporary files, too, but I could not
find where the temporary files are located. Is there a separate
directory? I have found a "pgsql_tmp" directory inside of the database
directories ("base/<oid>/pgsql_tmp"). Is this what I'm looking for?
Thanks for your help!

Regards,
Christian

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