Running on multiple core server

Hi,

I just bought a DELL Xeon with Quad Cores and installed it with Debian
Stable. I tested this server to run my web application written with
PHP5 with PostgreSQL 8.3 as the rdbms.

While retrieving a complex report on client machine using a web
browser, that took a few minutes, I ran htop on the server which shows
the CPU core's activities. It showed Apache2 and PostgreSQL working
furiously, but, only sharing a single core. The other 3 cores remained
idle.

However when I ran the query simultaneous from a 2nd client, it used
another core for this. And a 3rd core was used when I ran another
query from a 3rd client, running simultaneously.

Why doesn't the OS make use of the other 3 cores - assigning one to
Apache and another to PostgreSQL when only 1 client is querying?

uname -a shows
Linux pcserver 2.6.26-2-686 #1 SMP Mon Aug 30 07:01:57 UTC 2010 i686 GNU/Linux

Is there anything I can do to tweak?

--
Jason Tan Boon Teck