This assumes a *nix OS. Requirements (particularly software) will be
different on Windows.

Software:
PostgreSQL 7.4 or higher (http://www.postgresql.org)
GNU awk (http://www.gnu.org)
perl v5 or higher (http://www.perl.com)
perl DBI library
ftp://cpan.org/modules/by-category/07_Database_Interfaces/DBD/DBD-Pg-1.32.readme
ftp://cpan.org/modules/by-category/07_Database_Interfaces/DBD/DBD-Pg-1.32.tar.gz
perl DBD::Pg PostgreSQL interface for DBI
ftp://cpan.org/modules/by-category/07_Database_Interfaces/DBI/DBI-1.43.readme
ftp://cpan.org/modules/by-category/07_Database_Interfaces/DBI/DBI-1.43.tar.gz

Note - you must install the DBI package first, then the DBD::Pg package.

If you need to build PostgreSQL, you will need:
GNU make (3.76.1 or later)
ISO/ANSI C compiler (gcc recommended)
gzip
GNU readline (preferred but not required)

All of the above packages are available at http://www.gnu.org.

Hardware:
No specific requirements other than those associated with the OS.
Memory - no defined minimum, but more memory == less disk IO == better
performance

Disk Space:
100MB for CONCEPT installation directory
65MB for PostgreSQL source tree
15MB for PostgreSQL installation directory
90MB for regression tests (for building PostgreSQL)
25MB for an empty database cluster

Not Required But Highly Recommended:
If you use Windows in addition to the *nix machine that is running
PostgreSQL, install the PostgreSQL ODBC driver on your Windows machine
so you can view the database through a program like Microsoft Access.
If not, then download and install one of the graphical interfaces listed
at http://techdocs.postgresql.org/guides/GUITools.

Development Platform:
Intel Pentium M 1.6GHz
512MB Ram
512MB Swap
12GB HD
Red Hat Linux 9
PostgreSQL 7.4.1
perl 5.8.0