"timestamp without timezone" and at "time zone"

I'm seeing some odd behavior (to me) around a timestamp without timezone
column.  Was hoping someone could shed some light on this for me.  I
insert current_timestamp into the column.  When I select the value it is
the expected UTC time.  When I select the value with "AT TIME ZONE EDT"
I expected it to return in eastern time which is UTC - 4, but is
returning as UTC + 4.  Is AT TIME ZONE incompatable with this data type?

Postgres 8.1.11
OS time is UTC
Postgres timezome is UTC

I did the below example at 12:58 eastern time.  UTC time was 16:58.

I have a table with a column timestamp without timezone.

matthew/[local] hdap=# \d  billing.stefan_test;
           Table "billing.stefan_test"
 Column |            Type             | Modifiers
--------+-----------------------------+-----------
 dt     | timestamp without time zone |

I insert a record.
INSERT INTO billing.stefan_test(dt)
    VALUES (CURRENT_TIMESTAMP);

matthew/[local] hdap=# select dt, dt AT TIME ZONE 'EDT' from
billing.stefan_test;
             dt             |           timezone
----------------------------+-------------------------------
 2008-10-17 16:58:51.240091 | 2008-10-17 20:58:51.240091+00    <<< Was
expecting 12:58:51
(1 row)