language "plpgsql" does not exist

Hi everybody.
I'm a new born in the PostGreSQL domain (usually deal with Oracle or SQL
Server) and I got the following error when trying to create a function using
the default language plpgsql: language "plpgsql" does not exist
I was not able to find clues on the net to help me to solve this problem,
that's why I'm sending this post now.

I just installed the version 7.3.4 of PostGreSQL (basic installation).

Here the source of the function I try to create:
-------------
CREATE OR REPLACE FUNCTION ts_groupEdit
(VARCHAR,INTEGER,VARCHAR,VARCHAR,INTEGER,INTEGER) RETURNS INTEGER AS '

DECLARE
vi_name ALIAS FOR $1;
vi_companyId ALIAS FOR $2;
vi_description ALIAS FOR $3;
vi_rights ALIAS FOR $4;
vi_debug ALIAS FOR $5;
v_groupId INTEGER;
BEGIN
SELECT groupId INTO v_groupId
FROM Groups
WHERE companyId=vi_companyid AND
name=vi_name;

IF v_groupId IS NOT NULL THEN
UPDATE GROUPS SET description=vi_description
WHERE groupId=v_groupId;
ELSE
INSERT INTO Groups (companyId, name, description)
VALUES (vi_companyid, vi_name, vi_description);
END IF;

RETURN 0;
END; '
LANGUAGE 'plpgsql';
-------------

Any help will be welcome.
May be I have to load or install the plpgsql module, but I didn't find such
instruction in the documentation so I guess it is there by default.

Seb.

--
Sébastien BAUDRY - DBA Oracle/MS-SQL & Project Manager
BAUDRY ENGINEERING BT. H-1025 Budapest Verhalom utca. 31/D. I/8.
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