Trouble with CREATE FUNCTION

Dear All,

I have tried creating a function as follows:

CREATE FUNCTION chkTelephone () RETURNS OPAQUE AS '  BEGIN     IF EXISTS (SELECT *                FROM tenant t                WHERE t.areacode = NEW.areacode AND                      t.telephone = NEW.telphone) THEN        RAISE EXCEPTION ''THAT TELEPHONE NUMBER ALREADY EXISTS!'';     END IF;     RETURN NEW;  END;
' LANGUAGE 'plpgsql';

However I get the following error:

ERROR:  Unrecognized language specified in a CREATE FUNCTION: 'plpgsql'.
Recognized languages are sql, C, internal and the created procedural
languages.

In the documentation it states that 'PL/pgSQL is a loadable procedural
language for the Postgres database system.'. Where can I load it from and
are there any other problems that may arise?

Cheers, Steve.