This site has been running Drupal 5 for over a year now, even though Drupal 6 has been available since February. I kept meaning to update it, but never got around to it. Of course, then along came Acquia and a pressing need to try out the new kid on the block (for purely professional reasons, of course). So, armed with proper backup tools and a fast Internet connection, I set about to sacrifice my blog on the alter of experimentation. Onwards!
The documentation, available right from the downloads page, is a fairly extensive and thorough PDF. Of particular note, it goes out of its way to specify PHP 5.2 and MySQL 5.0 as minimum requirements. Thank you, Acquia! (For RHEL 5 users, who are stuck with PHP 5.1, it does point out that most of Drupal will work but, for example, Date module will have reduced functionality.)
The documentation includes lots of screenshots. Database setup is guided through phpMyAdmin, which makes sense as it's the most likely tool that all users will have available on their host. It also goes out of its way to highlight edge-case caveats, such as "Safari 3 will extract the download files for you" and "remember that .htaccess file that most FTP clients don't!" Command line instructis are provided, too, for the l33t crowd.