how can I find out the numeric directory name of each database in PostgreSQL 8.3

Hi,

In PostgreSQL 7.x, I can use SQL:
select datname, oid from pg_database
to find out the numeric directory name under $PGDATA/base for each
database. But it doesn't work for PostgreSQL 8.3.
Is there any way I can do it for 8.3?

Thanks,
--
Justin Yao