Performance postgresql

Hi
sorry for my english
My serwer is:
 p4 2.4 Ghz, 1 GB RAM, data from postgres on RAID 0 SCSI
(hardware scsi)
some tables (about 15) have 50.000 position, and all data (pgdumpall) are
about 600 MB

I have apache 1.3.29 - and he use the database for generate pages.

So my problem is performance this database.

If I run e.g. Apache Benchmark - ./ab -c 1000 -n 100 http://some adres who
use the all tables
my system halt (load about 200) , i see so many postmaster proces...

my config:
tcpip_socket = true
max_connections = 512
shared_buffers = 31000
sort_mem = 2096
vacuum_mem = 20480
max_fsm_pages = 589824
max_fsm_relations = 32768
wal_buffers = 1024
checkpoint_segments = 4
checkpoint_timeout = 1800
checkpoint_warning = 30
commit_delay = 10
commit_siblings = 2
enable_indexscan = true
enable_seqscan = true
enable_sort = true
effective_cache_size = 20000
random_page_cost = 4

please for help