transaction in postgres

Hi averyone,
I'm using a new function to include two query into an unique transaction. Is
this the only way to do it? The following lines show you my function, the
purpose is to return the id_utente field (serial) of the last insert done:
----------------------------------------
CREATE FUNCTION "id_from_insert"("varchar", "varchar", "int4", "bpchar",
"varchar", "int4", "int4", "int4", "varchar", "int4", "bpchar", "varchar",
"varchar") RETURNS "int4" AS 'INSERT INTO g_registrazione_generale (
nome,
cognome,
data_di_nascita,
genere,
indirizzo,
codice_postale,
telefono,
id_documentazione,
email,
data_inserimento,
stato,
velocita_connessione,
istruzione
) VALUES (
$1,
$2,
$3,
$4,
$5,
$6,
$7,
$8,
$9,
$10,
$11,
$12,
$13
);
SELECT max(g_registrazione_generale.id_utente) FROM
g_registrazione_generale;
' LANGUAGE 'sql';
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Best regards