Indexes not being used.

Hello all. I'm having trouble convincing Postgres to use indexes created
after loading data into my database. Here's an example:

test=# create table test ( id integer, value text );
CREATE
test=# insert into test values ( 1, 'foo');
INSERT 14725127 1
test=# insert into test values ( 2, 'bar');
INSERT 14725128 1
test=# insert into test values ( 3, 'baz');
INSERT 14725129 1
test=# create index test_index on test (id);
CREATE
test=# explain select * from test where id = 1;
NOTICE: QUERY PLAN:

Seq Scan on test (cost=0.00..1.04 rows=1 width=16)

EXPLAIN

Now, this isn't a problem with just 3 rows, but in my real tables with
over a million records it's rendering my tables unusable. I can get
working indexes if I create them before loading data:

test=# create table test2 ( id integer, value text );
CREATE
test=# create index test2_index on test2 (id);
CREATE
test=# insert into test2 values ( 1, 'foo');
INSERT 14725165 1
test=# insert into test2 values ( 2, 'foo');
INSERT 14725166 1
test=# insert into test2 values ( 3, 'foo');
INSERT 14725167 1
test=# explain select * from test2 where id = 1;
NOTICE: QUERY PLAN:

Index Scan using test2_index on test2 (cost=0.00..8.14 rows=10 width=16)

EXPLAIN

I'll use this as a work-around for now but I'd really like to be able to
create new indexes after import. I'm doing some experimental data-mining
and it's not always possible to know upfront what indexes will be
necessary.

I'm using Postgres 7.1.2 on Linux 2.4.5, in case it matters.

-sam