What is Drupal?
Drupal is an open source CMF (Content Management Framework) created by Dries Buytaert.
What is the difference between a CMS and a CMF?
Not a lot but Drupal is refered to as a CMF due to is configurability and customisation that you are able to do through it's excellent back end and through the use of third party contributed modules as well as modules created by yourself.
How do I get Drupal?
Go to http://drupal.org and download which ever version you want.
Which version do I want?
Version 6 is the latest stable release but isn't widely used due to a lot of the contributed modules not being available. But given time this has changed and using 6 on a live site has become more feasible.
What do I need to run Drupal?
You need a web server that supports PHP and either a MySQL or PostgreSQL database.
Drupal supports both IIS and Apache, with Apache being the prefered and most tested web server.
Which version of PHP do I need?
It is recommended for Drupal 5.1 onwards to use PHP 5.2 to make use of certain new PHP functions.
What PHP configuration do I need to run Drupal properly?
To run Drupal with good performance the PHP memory limit should be set to no less than 8MB, with 16MB or more being prefered. Some contributed modules can need up to 96MB memory limit.
register_globals needs to be off.
session.save_handler set to user.
error_reporting set to E_ALL & ~E_NOTICE.
Additionally session.cache_limiter is recommened to be set to nocache.
If you have any other questions about the requirements of Drupal, please read the System requirements on the Drupal.org website.