Indexes not working, please help.

Hi there.

The table medidas has the following structure:

Table "medidas"
Column | Type | Modifiers
------------+-----------------------------+-----------------------------------------------------
cod | bigint | not null default
nextval('"medidas_cod_seq"'::text)
cod_ponto | bigint |
data_hora | timestamp without time zone |
valor | smallint |
tipo_ponto | bytea |
unidade | bytea |
Indexes: teste
Primary key: medidas_pkey

I populated it with 8859000 entries using many "100 inserts"
blocks transactions. Inserting data on the table is no problem.
Althought I created the "teste" index ( create index teste on
medidas (cod) ), vacuumed and analyzed the database, pgsql still doesn't
use indexes.

explain select * from medidas where cod = 1231232;
---
NOTICE: QUERY PLAN:

Seq Scan on medidas (cost=0.00..197590.50 rows=1 width=36)
---

I've read all the documentation I found, but I couldn't figure out
what's happening. Setting "enable_seqscan" to false doesn't help either.
This machine I'm working on won't be the production server, but
it's not that slow machine (P3 1GHz, 384MB, ATA 100) and without indexes
working, that select mentioned above takes almost 60 seconds to run...

[]'s
Ricardo.