Before You Start
The beginning is the most important part of the work - Plato
Drupal is a content management system. It is one component of a website architecture and relies on several other components to work properly and perform at its best. If you are looking for a web host carefully review the requirements section when evaluating their services.
Tip
Drupal 7 will be developed for PHP 5.2. While this does not apply to Drupal 5 or 6 it would reduce later complication to build new sites using PHP 5.2 if possible.