Problem on Linux

I'm migrating tables from Solaris to Linux.  Other than Red-Hat moving the
directories a little bit I expected a close match on performance.

It seems that the SUN version (compiled from source) handled 13 million rows
with ( I know this is not efficient ) Select * from tableName;
The Linux box bumped me out of psql with the exact table structure but with
only 4 million rows doing the same select *.

I'm wondering if it is the startup of the system.  I had to issue a huge
nohup on the SUN and on linux it has a predefined /etc/rc.d/init.d script.

Linux postgres gurus'  -  I will have approx. 24 million rows per table
loaded each day.   I don't care if it takes 4 hours to complete an sql call
as long as it does complete.  I need to keep 90 days of data, so I'm
thinking of using a new (exact duplicate of) table each day for 90 days then

Truncate the oldest and start over.

Is there a better way?  And how do I tune the stock RedHat version?  I
really don't want to have to load it again from scratch (source).

P.S. I'm going from a 450MHz sparc to a 750MHz  compaq with similar amounts
of real and swap memory.

-Mark