The phpBB, the PHP based Bullet In Board) is a high powered, fully scalable and highly customizable open-source bulletin board package. phpBB has a user friendly interface, simple and straightforward administration panel, and helpful FAQ.
Based on the powerful PHP server language and choice among MySQL, MS-SQL, PostgreSQL or Access/ODBC database servers, phpBB is the ideal free community solution for all web sites.
The Unix/Linux and Windows OS based installation are the same since the software package depends and requires only Web server and MySql services which exists for both platforms.
The platform dependent version can be downloaded at: http://www.phpbb.com/downloads/
Once the correct version is downloaded it's contents should be decompressed, as it would come within the zip or tar.gz archive, within the apache's accessible folder, for example under the main web folder within the subfolder phpbb2 which should be created for easier use of the forum later.
After the decompressing the contents of the archive at the desired folder with the web browser access to the folder with the installation scripts should be attempted. If the page is correctly accessed the installation initial screen would appear like at the screen below.