It’s pretty simple to install phpBB from subversion, but I couldn’t find any instructions online, so I decided to write some.
Firstly, checkout the phpBB 3.0.x branch directory which always contains the latest stable code. You can do this with the following command:
svn checkout http://code.phpbb.com/svn/phpbb/branches/phpBB-3_0_0/phpBB forum
Where forum is the directory you want to install the forum into. Once all the code has been checked out, visit the the forum url in your web browser.
This will take you to an install wizard, which will guide you through the remaining steps. It’s as simple as that!