You will need PHP compiled and installed on your system. You will also need MySQL, PostgreSQL or Oracle setup.
If you are planning on using the email system, you will need to have an IMAP server installed and IMAP support compiled into PHP, or a POP3 server installed. You can have it installed as an Apache module or CGI mode for other web servers, the Apache module is preferred. We will assume that you are running on a Linux or other Unix system for these steps. Windows is supported, but there is no documentation for it currently.
Seek3r has tested:
phpGroupWare.org runs: Red Hat 6.2, Apache/1.3.12,PHP/4.0.2,mod_perl/1.21,MySQL 3.23.10-alpha,Courier-IMAP 0.33+ with qmail 1.03
phpGroupWare.net runs: Red Hat 6.2,Apache/1.3.14 PHP/4.0.3pl1 mod_ssl/2.7.1 OpenSSL/0.9.6 PHP4.03.pl1, MySQL 3.23.10-alpha,qmail 1.03
dev boxes are variants on: Red Hat 7.0,mysql-3.23.22-6 (from RH7 RPM), and Sendmail, Courier, or qmail+courier IMAP depending on mood.
main test box: Red Hat 6.2,Apache 1.3.12,PHP 3.0.16,PostgreSQL 7.2,Sendmail (from RH6.2)
laptop is rh 6.1, apache 1.3.?, MySQL and PostgreSQL 7.0 w/ PHP 3.0.16, its a P-90 w/ 40 mb ram and a 800 mb hd
Test box: Win2k with IIS5.0, PHP4.0.2 and MySQL