Help tuning query

All;

Can anyone please help with the tuning of this query?
With 77000 rows in the operator_messages database the query is taking almost
15 seconds to return.  Preference woul dbe under 5 seconds if possible.
System load on a dual processor P3 with 1.5GB of memory remains under .4
during the query.
The query and explain are noted below as well as description of the tables;
Note both ANALYZE and VACUUM have been run numerous times.
any help would be appreciated.   -Kev


virgin=# explain SELECT opr.msg_id, opr.status, opc.std_time
virgin-# FROM op_msg_folder opc, operator_messages opr
virgin-# WHERE opr.username = 'khp'
virgin-# AND opr.foldername = 'inbox'
virgin-# and opr.msg_id = opc.msg_id;
NOTICE:  QUERY PLAN:

Merge Join  (cost=25037.29..27675.47 rows=47958 width=54) ->  Index Scan using opmf_i on op_msg_folder opc
(cost=0.00..1797.37
rows=48579 width=32) ->  Sort  (cost=25037.29..25037.29 rows=47958 width=22)       ->  Seq Scan on operator_messages
opr (cost=0.00..20722.26
 
rows=47958 width=22)

virgin=# \d operator_messages      Table "operator_messages"  Column   |     Type     | Modifiers
------------+--------------+-----------msg_id     | numeric      |username   | text         |foldername | text
|status    | character(1) |
 
Indexes: op_msgs_i,        opr_msgs_foldername_i,        opr_msgs_username_i

virgin=# \d op_msgs_i
Index "op_msgs_i"Column |  Type
--------+---------msg_id | numeric
btree

virgin=# \d opr_msgs_foldername_i
Index "opr_msgs_foldername_i"  Column   | Type
------------+------foldername | text
btree

virgin=# \d opr_msgs_username_i
Index "opr_msgs_username_i" Column  | Type
----------+------username | text
btree

virgin=# \d op_msg_folder          Table "op_msg_folder"    Column     |     Type     | Modifiers
----------------+--------------+-----------msg_id         | numeric      |status         | character(1) |std_time
|text         |julian_time    | text         |smi            | character(3) |description    | text         |type
  | text         |flight         | text         |tail           | text         |dep_station    | text
|dest_station  | text         |op_description | text         |
 
Unique keys: opmf_i

virgin=# \d opmf_i; Index "opmf_i"Column |  Type
--------+---------msg_id | numeric
unique btree