This is the PostgreSQL Installer for Windows. 

postgresql-8.3.20-1.zip is the multi-language version of the installer. 

postgresql-8.3.20-1-binaries-no-installer.zip is a zip of the PostgreSQL 
installation directory. It does not include any of the bundled apps or
drivers and is intended for expert users only! This bundle requires the 
Microsoft Visual C++ 8.0 runtimes to be installed on your system. A 
seperate installer can be downloaded from:

http://www.microsoft.com/downloads/details.aspx?FamilyID=200b2fd9-ae1a-4a14-984d-389c36f85647&DisplayLang=en

postgresql-8.3.20-1-symbols.zip is a zip of the debug symbols for 
PostgreSQL.

Each file has been GPG signed (see the accompanying .sig files) at build 
time by Dave Page. Dave's public key may be found at
http://www.pgadmin.org/pgp/davepage.pgp

A walkthrough of the installation may be found at:
 - http://pginstaller.projects.postgresql.org/

The FAQ may be found at:
 - http://pginstaller.projects.postgresql.org/faq/FAQ_windows.html
 - http://pginstaller.projects.postgresql.org/faq/FAQ_windows_br.html
     (Brazilian Portuguese translation)
 - http://pginstaller.projects.postgresql.org/faq/FAQ_windows_ja.html
     (Japanese translation)
 - http://pginstaller.projects.postgresql.org/faq/FAQ_windows_tr.html
     (Turkish translation)
        
Details of how to run a silent installation may be found at:
 - http://pginstaller.projects.postgresql.org/silent.html
          
The pgInstaller project may be found at: 
 - http://pgfoundry.org/projects/pginstaller/