This section holds the most general questions about PHP: what it is and what it does.
From the preface of the manual:
PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly.
A nice introduction to PHP by Stig Sæther Bakken can be found here on the Zend website.
PHP/FI 2.0 is an early and no longer supported version of PHP. PHP 3 is the successor to PHP/FI 2.0 and is a lot nicer. PHP 4 is the latest generation of PHP, which uses the Zend engine under the hood.
Yes. See the INSTALL file that is included in the PHP 4 source distribution.
There are a couple of articles written on this by the authors of PHP4. Here's a list of some of the more important new features:
Extended API module.
Generalized build process under UNIX
Generic web server interface that also supports multi-threaded web servers
Improved syntax highlighter
Native HTTP session support
Output buffering support
More powerful configuration system
Reference counting
You should go to the PHP Bug Database and make sure the bug isn't a known bug. If you don't see it in the database, use the reporting form to report the bug. It is important to use the bug database instead of just sending an email to one of the mailing lists because the bug will have a tracking number assigned and it will then be possible for you to go back later and check on the status of the bug. The bug database can be found at http://bugs.php.net/.