All opinions here sound good so I decided to use only one db engine
(PostgreSQL 8.1) and two databases; now I must tune my database
generator parameters (I use PowerDesigner by Sybase) in order to
work-arround the pg's identifier case sensitivity (newsgroups app (php
scripts) doesn't use quotes (developed against MySQL) but the
PowerBuilder app for company data uses quotes and mixed case of
identifiers (developed against Sybase SQL Anywhere)). Thank you all for
sharing all your experience and your time.
Ivo