Running Postgres Daemons with same data files

Dear All,

I am working in Linux 8.0 and running postgresql 7.2. I am trying to
access same data files from the two postgres daemons. I mean there are
two PC's running with postgres and one NAS server where data files are
kept. To run postgres on the machines I first mount the NAS file system
and then run it like

shell>postmaster -D $(PATH_TO_DATA_FILE)

Daemons are running well but there is problems with synchronization of
the data files i.e when i insert some tuples in the tables its not
immediately writing then to file its kept in the cache only and when I
try to see from the other machine its displaying the old tuples.

I want after every transaction or query the database update the data
files, how can I do this? And always read from the data files for select
operations. My main aim is no cache operation to use the postgres as
file system(for every operation file operations only), I know it will
degrade the database performance but its the requirement OR if there is
any other way by which I can achieve this, please tell me.

regards
bhartendu