slow database - Mailing list pgsql-performance

my data base is very slow. The machine is a processor Xeon 2GB with
256 MB of RAM DDR. My archive of configuration is this:

================================================================

#
# PostgreSQL configuration file
# -----------------------------
#
# This file consists of lines of the form:
#
#   name = value
#
# (The '=' is optional.) White space may be used. Comments are introduced
# with '#' anywhere on a line. The complete list of option names and
# allowed values can be found in the PostgreSQL documentation. The
# commented-out settings shown in this file represent the default values.
#
# Any option can also be given as a command line switch to the
# postmaster, e.g. 'postmaster -c log_connections=on'. Some options
# can be changed at run-time with the 'SET' SQL command.
#
# This file is read on postmaster startup and when the postmaster
# receives a SIGHUP. If you edit the file on a running system, you have
# to SIGHUP the postmaster for the changes to take effect, or use
# "pg_ctl reload".
#========================================================================


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

max_connections = 50
superuser_reserved_connections = 2

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

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

#virtual_host = ''

#krb_server_keyfile = ''

#
#       Shared Memory Size
#
shared_buffers = 5000           # min max_connections*2 or 16, 8KB each
max_fsm_relations = 400         # min 10, fsm is free space map, ~40 bytes
max_fsm_pages = 80000           # min 1000, fsm is free space map, ~6 bytes
max_locks_per_transaction = 128 # min 10
wal_buffers = 4         # min 4, typically 8KB each

#
#       Non-shared Memory Sizes
#
sort_mem = 131072               # min 64, size in KB
#vacuum_mem = 8192              # min 1024, size in KB


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


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

effective_cache_size = 170000   # typically 8KB each
random_page_cost = 1000000000   # units are one sequential page fetch cost
cpu_tuple_cost = 0.3            # (same)
cpu_index_tuple_cost = 0.6      # (same)
cpu_operator_cost = 0.7         # (same)

default_statistics_target = 1   # range 1-1000

#
#       GEQO Optimizer Parameters
#
geqo = true
geqo_selection_bias = 2.0       # range 1.5-2.0
geqo_threshold = 2000
geqo_pool_size = 1024           # default based on tables in statement,
                                # range 128-1024
geqo_effort = 1
geqo_generations = 0
geqo_random_seed = -1           # auto-compute seed


#
#       Message display
#
server_min_messages = fatal     # Values, in order of decreasing detail:
                                #   debug5, debug4, debug3, debug2, debug1,
                                #   info, notice, warning, error, log, fatal,
                                #   panic
client_min_messages = fatal     # Values, in order of decreasing detail:
                                #   debug5, debug4, debug3, debug2, debug1,
                                #   log, info, notice, warning, error
silent_mode = false

log_connections = false
log_pid = false
log_statement = false
log_duration = false
log_timestamp = false

#log_min_error_statement = error # Values in order of increasing severity:
                                 #   debug5, debug4, debug3, debug2, debug1,
                                 #   info, notice, warning, error, panic(off)


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

#explain_pretty_print = true

# requires USE_ASSERT_CHECKING
#debug_assertions = true


#
#       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_statement_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
#
#autocommit = true
#dynamic_library_path = '$libdir'
#search_path = '$user,public'
datestyle = 'iso, us'
#timezone = unknown             # actually, defaults to TZ environment setting
#australian_timezones = false
client_encoding = sql_ascii     # actually, defaults to database encoding
authentication_timeout = 1      # 1-600, in seconds
deadlock_timeout = 100          # in milliseconds
#default_transaction_isolation = 'read committed'
#max_expr_depth = 1000          # min 10
#max_files_per_process = 1000   # min 25
#password_encryption = true
#sql_inheritance = true
#transform_null_equals = false
#statement_timeout = 0          # 0 is disabled, in milliseconds
db_user_namespace = false



#
#       Locale settings
#
# (initialized by initdb -- may be changed)
LC_MESSAGES = 'en_US'
LC_MONETARY = 'en_US'
LC_NUMERIC = 'en_US'
LC_TIME = 'en_US'


================================================================


somebody please knows to give tips to me to increase the
performance