To successfully install and use Joomla! you must have a fully operational web server (Apache is the optimum), a database (MySQL is the optimum) and the server side scripting language PHP together with specific modules that are activated within PHP for MySQL, XML, and Zlib functionality amongst others.
Whilst the community will always do its best to help you resolve issues that you may experience, Joomla! is not a web server in its own right and depends on you having a fully functioning & compatible Web server.

You must ensure that you have the MySQL, XML, and Zlib functionality enabled within your PHP installation. This is controlled within the php.ini file.

Do not use PHP 4.3.9, PHP 4.4.2 or PHP 5.0.4; these releases have known bugs that will interfere with the installation of Joomla! There was also an issue with the Zend Optimizer Version 2.5.10 for PHP 4.4.x. You should ask your host to upgrade to a later release as soon as possible where applicable.
If you experience problems with Joomla! on other versions of these source server programs please take the time to check out the changelogs for your particular version, as there are often good indicators of the likely cause of issues. If there is a particular problem identified you need to notify your Host provider and encourage them to update the affected program

MySQL 6.x is not yet supported.

Joomla! has been successfully tested on many variants within the main three OS for Windows, Linux, Apple Mac OSX. It may well work on other platforms but this is less well documented.

Joomla! is also regularly used and tested through the main web browsers available such as IE6 +, Firefox 1.5 +, Safari, and Opera but it may also work with others.