separating out database files

How do you separate the postgresql database files in InterChange
from the rest of the application?

What is the command syntax and what files need to be modified that
call and point to the database? I am researching DSN...

My goal is to separate InterChange so it can exist on three
different machines representing a three tier architecture -
web tier, middle tier, and data tier (backend database).

I only want the minimum number of files required on the database
server. Therefore what files are required and which ones can
moved to the other machines? Is there a FAQ on this somewhere?

Are there any gotchas to look out for when doing this?

Specs: Server RedHat 7.1 2.4.2-2 kernal everything build with
Interchange 4.8

I am learning Linux and Postgresql from scratch.

Thanks,
Jeff