Query optimization

Greetings!

I am trying to find a way to optimize this query and have hit a wall.  The
database size is 2.9 GB and contains 1 million records.  The system is a
dual xeon 1 ghz P3 with 4 GB ram, 2 of it shared memory.  Redhat linux
kernel 2.4.18-5 ext3fs.

I'm hoping I haven't hit the limit of the hardware or os but here's all
the relevant info.  Questions, comments, solutions would be greatly
appreciated.

11696 postgres  25   0 1084M 1.1G  562M R    99.9 28.6   2:36 postmaster

Postgresql.conf settings
shared_buffers = 250000
sort_mem = 1048576            # min 32
vacuum_mem = 128000          # min 1024
wal_files = 64 # range 0-64
enable_seqscan = false
enable_indexscan = true
enable_tidscan = true
enable_sort = true
enable_nestloop = true
enable_mergejoin = true
enable_hashjoin = true

[postgres@db1 base]$ cat /proc/sys/kernel/shmmax
2192000000

database=# explain analyze SELECT active,registrant,name FROM person WHERE
object.active = 1 AND object.registrant = 't' ORDER BY UPPER(object.name)
DESC LIMIT 10 OFFSET 0;
NOTICE:  QUERY PLAN:

Limit  (cost=nan..nan rows=10 width=2017) (actual
time=204790.82..204790.84 rows=10 loops=1)
  ->  Sort  (cost=nan..nan rows=1032953 width=2017) (actual
time=204790.81..204790.82 rows=11 loops=1)
        ->  Index Scan using registrant__object__idx on object
(cost=0.00..81733.63 rows=1032953 width=2017) (actual
time=0.14..94509.14 rows=1032946 loops=1)
Total runtime: 205125.75 msec

NOTICE:  QUERY PLAN:

Limit  (cost=nan..nan rows=10 width=2017) (actual
time=204790.82..204790.84 rows=10 loops=1)
  ->  Sort  (cost=nan..nan rows=1032953 width=2017) (actual
time=204790.81..204790.82 rows=11 loops=1)
        ->  Index Scan using registrant__object__idx on object
(cost=0.00..81733.63 rows=1032953 width=2017) (actual
time=0.14..94509.14 rows=1032946 loops=1)
Total runtime: 205125.75 msec