If the VPOP3 computer has a version of PostgreSQL older than version 8.3 installed for other software, and you can't/don't want to remove that you need to set up the PostgreSQL 8.3 or later for VPOP3 to use a different TCP/IP port number.
The VPOP3 installer can't do this for you, so you have to do it manually
Install PostgreSQL manually onto the alternative port
After installing PostgreSQL onto the alternative port, tell
Now you need to create the database user/database in the NEW version of PostgreSQL. The installer can't do this for you if it is on a different port.
Open up a command prompt in Windows and find the 'bin' subdirectory of the PostgreSQL installation directory (eg either VPOP3\pgsql\bin or c:\program files\postgresql\8.3\bin or wherever) Type: psql -U postgres -p <new port number> For the password use 'pgsqlpass' (or use a different -U <username> and password value if you created a different superuser when setting up Postgres manually)
Then in the postgresql prompt type: CREATE USER vpop3 LOGIN PASSWORD 'vpop3pass'; CREATE DATABASE vpop3 OWNER=vpop3;
Finally, install VPOP3, and tell the installer not to install PostgreSQL.