Performance Problem Index Ignored, but why

I've the task of porting a current Oracle application to PostgreSQL.

Database: 7.2.1
OS: Linux 2.4.9-13smp

I've an odd thing happening with a query. Using a simple table:

Table "state_tst"
Column | Type | Modifiers
---------+----------------------+-----------
id | integer | not null
v_state | character varying(2) |
f_state | character(2) |
Indexes: st_f_state_idx,
st_v_state_idx
Primary key: state_tst_pkey

id is a sequence number and primary key, v_state and f_state are 2
character U.S. States. I created v_state as varchar(2) and f_state as
char(2) to test if the query explained/performed differently (it
doesn't).

CREATE INDEX st_v_state_idx ON state_tst USING btree (v_state);
CREATE INDEX st_f_state_idx ON state_tst USING btree (f_state);

Load the table using a copy from ...

vacuum verbose analyze state_tst;

Total rows: 14309241

Queries using either f_state = or v_state = explain (and appear to
execute) using a sequential scan. Resulting in 60 - 80 second query
times.

Can I force the use of an index? Or do I have something wrong? Any
ideas?

pg_test=# explain select count(*) from state_tst where f_state = 'PA';
NOTICE: QUERY PLAN:

Aggregate (cost=277899.65..277899.65 rows=1 width=0)
-> Seq Scan on state_tst (cost=0.00..277550.51 rows=139654
width=0)

EXPLAIN