Renaming a DB

Hi all,
I'm running a Postgres 7.3.3 and I had the necessity to
rename a DB, I did this by updating the pg_database
table.
If I perform psql -l I'm able to see that is reported the
correct name ( I guess because a select on pg_database
table is performed ) but if I try to connect to the DB
after the renaming I obtain the error:

psql: FATAL: Database "new_name" does not exist in
the system catalog.

however trying after a while ( without do nothing ) I'm
able to connect to "new_name" database, is like the names
of database are cached somewhere and this cache expire
after a while.

Any idea ?

Regards
Gaetano Mendola