Drupal 4.x Multi-site Configuration How-to

In February 2006, I found Drupal and decided to give it a try. Since then, I have implemented five drupal sites of my own and three for clients, some independent of each other and some that share data. Between then and now, I have done a lot of research, testing, trying, trouble-shooting, and designing.
I have decided to share some general processed used to implement certain functions in these sites. Click-by-click procedures are not included as implementation environments differ (a big lesson learned over the past year).