Rules on 8.0.2

Hi, I'm trying create the rule :

CREATE OR REPLACE RULE select_public_cliente AS ON SELECT TO
public.cliente_tipo
WHERE NOT EXISTS ( SELECT usesysid FROM pg_user left join pg_group on (
idx( grolist, usesysid ) > 0 )
WHERE usename = current_user
ANDgroname SIMILAR
TO 'assinatura' )
DO INSTEAD SELECT clt_dsc_tipo FROM public.cliente_tipo;

Its to limit users to see only one column on table. But I've the
error:

ERROR: event qualifications are not implemented for rules on SELECT

The version is: PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC
gcc (GCC) 3.3.5 (Debian 1:3.3.5-5)

Any idea?

--
William Leite Araújo