Lack of Performance

Hi all!

I wonder if there is any possibilty to boost the performance of my
postgresql machine. I used to have it running on a dual p3-450 + 512mb ram
(with apache/php on the same machine). Recently I moved it to a new machine,
p3-800 + 512mb ram, and moved the apache to another machine.

Now the performance is somewhat BAD. The load of the machine is arround
10.00 and the postmaster processes are taking all of the machines cpu power.
I don't have correct stats to my hand but the web server is currently
handling something about 220.000 page impressions per day (220.000 page
calls which open a php -> db connection running at least 1 query).

I didn't went to deep into query optimization yet cause I didn't read enough
about that now. So I tried adjusting the command line options ....

What are the best values to use for sort_mem and shmem_buffers?

I'm currently starting the service with

-B 256
-i
-N 48
-o '-F -S 512'

This seems NOT to be the right value but I don't know it what way I can
experiment with them?

If somebody has some tips handy i'd like to hear them.

Thanks,
Thomas