any way to make query use index?

I am working through our application looking for ways to eliminate seq
scans in our database.  I am looking for some help with this query.

SELECT rev_desc FROM rev_code_desc WHERE rev_code = lpad('0300', 4, '0')

Is there anyway to make postgres use an index on this query?

Here is the table definition:
CREATE TABLE rev_code_desc
(
  rev_code character(4) NOT NULL,
  rev_desc text,
  user_id character varying(12),
  live_rec boolean DEFAULT true,
  CONSTRAINT rev_code_desc_pkey PRIMARY KEY (rev_code)
)

Right now, I can't seem to get it to use an index for this type of
query.  Of course, in our application it is SELECT rev_desc FROM
rev_code_desc WHERE rev_code = lpad(, 4, '0').

Thanks for any help,

Chris

PG 8.1.3