A new command in Drush 5 is the core-quick-drupal command (alias “qd”) – the purpose of this command is to get you running in Drupal with zero setup. All you need is php-cgi and the PDO sqlite driver – you don’t need MySQL or Apache running at all. Running the command will download and install Drupal (or your choice of distribution) as well as any contrib projects you like, start the built in php webserver and open your default browser with you already logged in as user 1. Fun stuff.
Also, you may want to check out the runserver screencast for more detail on using the built in webserver. Please share any feedback or questions in the comments.