database tuning

Howdy:

I'm running PostgreSQL 7.2.1 on Redhat Linux 7.2
kernel 2.4.7-10.

I have a question about performance tuning
with PostgreSQL.

A few weeks ago, I installed and migrated data
from version 7.1.3 to version 7.2.1. After that,
it seems that when I load data, have users do
a select / insert / or otherwise access the
database, it takes a very long time to complete.

When looking at the processes with 'top', what
used to happen was whatever was running would take
all of the resources (or, whatever was available);
so, if there were say, four 'selects' from the
database, there would be four processes fighting
for CPU time. Now it seems that the processes
are more idle and are not using the CPU as effectively
and efficiently as they could.

How can I change this? What can I do to tune
the database more efficiently?

Thanks!

-X