Please help me with pg_hba.conf file settings

Dear Sir
Hello!
I have a Linux web server on which I am providing name based hosting
services to my clients.
I want that my clients who have their virtual sites on my server should
be able to connect to their databases by using php or any other
server side programs to connect to postgresql database thourgh their
password authentications.

For this I edited the pg_hba.conf file of Postgresql which is at the
location /var/lib/pgsql/pg_hba.conf and I added the following lines
at the bottom of this file using vi editor.

host all 64.65.7.145 255.255.255.255 trust

By adding the above file in pg_hba.conf file my clients are able to
connect to their databases but even if they give any wrong password
in their server side programs which they are using to connect to
their database they are able to access their databse.

I tried adding the following lines to pg_hba.conf file :

host all 64.65.7.145 255.255.255.255 password pgpass

I created pgpass by the command pg_passwd pgpass and added
the user (i.e my client username and password) but it did not
work. though this way it is working fine on my local intranet
which is on Linux.

Please help me solve my problem.
Regards