Performance question..

All,
I'm looking for ideas on tweaking pgsql.. here is my machine stats

Processor 0 runs at 550 MHz
Processor 1 runs at 550 MHz
Page Size : 4096
Phys Pages: 131072
Total Physical memory = 536870912 (512MB)

This is running on HPUX 11

Below is my postmaster.conf file

#
# Connection Parameters
#
#tcpip_socket = false
tcpip_socket = true
#ssl = false

max_connections = 64

#port = 5432
#hostname_lookup = false
#show_source_port = false

#unix_socket_directory = ''
#unix_socket_group = ''
#unix_socket_permissions = 0777

#virtual_host = ''

#krb_server_keyfile = ''

#
# Shared Memory Size
#
shared_buffers = 128 # 2*max_connections, min 16
#max_fsm_relations = 100 # min 10, fsm is free space map
#max_fsm_pages = 10000 # min 1000, fsm is free space map
#max_locks_per_transaction = 64 # min 10
#wal_buffers = 8 # min 4

#
# Non-shared Memory Sizes
#
#sort_mem = 512 # min 32
#vacuum_mem = 8192 # min 1024

#
# Write-ahead log (WAL)
#
#wal_files = 0 # range 0-64
#wal_sync_method = fsync # the default varies across platforms:
# # fsync, fdatasync, open_sync, or open_datasync
#wal_debug = 0 # range 0-16
#commit_delay = 0 # range 0-100000
#commit_siblings = 5 # range 1-1000
#checkpoint_segments = 3 # in logfile segments (16MB each), min 1
#checkpoint_timeout = 300 # in seconds, range 30-3600
#fsync = true

#
# Optimizer Parameters
#
#enable_seqscan = true
#enable_indexscan = true
#enable_tidscan = true
#enable_sort = true
#enable_nestloop = true
#enable_mergejoin = true
#enable_hashjoin = true

#ksqo = false

#effective_cache_size = 1000 # default in 8k pages
#random_page_cost = 4
#cpu_tuple_cost = 0.01
#cpu_index_tuple_cost = 0.001
#cpu_operator_cost = 0.0025

#
# GEQO Optimizer Parameters
#
#geqo = true
#geqo_selection_bias = 2.0 # range 1.5-2.0
#geqo_threshold = 11
#geqo_pool_size = 0 # default based on #tables in query, range 128-1024
#geqo_effort = 1
#geqo_generations = 0
#geqo_random_seed = -1 # auto-compute seed

#
# Debug display
#
#silent_mode = false

#log_connections = false
#log_timestamp = false
#log_pid = false

#debug_level = 0 # range 0-16

#debug_print_query = false
#debug_print_parse = false
#debug_print_rewritten = false
#debug_print_plan = false
#debug_pretty_print = false

# requires USE_ASSERT_CHECKING
#debug_assertions = true

#
# Syslog
#
# requires ENABLE_SYSLOG
#syslog = 0 # range 0-2
#syslog_facility = 'LOCAL0'
#syslog_ident = 'postgres'

#
# Statistics
#
#show_parser_stats = false
#show_planner_stats = false
#show_executor_stats = false
#show_query_stats = false

# requires BTREE_BUILD_STATS
#show_btree_build_stats = false

#
# Access statistics collection
#
#stats_start_collector = true
#stats_reset_on_server_start = true
#stats_command_string = false
#stats_row_level = false
#stats_block_level = false

#
# Lock Tracing
#
#trace_notify = false

# requires LOCK_DEBUG
#trace_locks = false
#trace_userlocks = false
#trace_lwlocks = false
#debug_deadlocks = false
#trace_lock_oidmin = 16384
#trace_lock_table = 0

#
# Misc
#
#dynamic_library_path = '$libdir'
#australian_timezones = false
#authentication_timeout = 60 # min 1, max 600
#deadlock_timeout = 1000
#default_transaction_isolation = 'read committed'
#max_expr_depth = 10000 # min 10
#max_files_per_process = 1000 # min 25
#password_encryption = false
#sql_inheritance = true
#transform_null_equals = false