Once you've been developing Drupal modules for any length of time you find that you need to test code on multiple versions of Drupal. The easiest way to do this is have separate Drupal releases running as virtual hosts. In this guide I'll walk though setting up Apache virtual hosts for Drupal 5 and Drupal HEAD. I'm assuming you're running Windows 2000 or greater and that you've already gotten Apache, MySQL and PHP setup and running on your local machine.