This post is in the writing stage as my new multisites are being built.. I assume this write up should be mostly complete by March 1st 2010..

This is one site of a multi site install of Drupal 6 on a shared host.
** This setup is very easy to do ... 
One thing to keep in mind.. There are many different ways to accomplish a given task with Drupal.

It is best to decide if the sites are going to have the same content or different content.
-The same content might be for different domains(.org .com .net and so on)
-or different content, such as this set up

I have been a re-seller for many years as ( http://www.OneLakesideWeb.com ) Anyway, it is a nice host and each account has a really nice control panel. Just like my clients, I have an account on the host too and needed to consolidate some of my sites. Since I have so many domains, I might as well do a multi-site with Drupal.
The shared host set up is not so nice for Drupal due to the constant need for Drupal to suck info from the database. Many shared hosts use a shared database server as well as a shared web server.
> To make pages load fast on a shared host setup I am using project/boost.

A few of the domains included in this install

Why all these domains? They are cheap when GoDumy has a sale.

http://www.davebeall.me
http://www.davebeall.info
http://www.davescanvas.com
http://www.davebeall.name
There are more domains associated with this install. But they are not be published here.

-- The write-up --

The basic set up I am using

This set-up uses one Drupal code base, one database with each site using a prefix_ during install. Each site has it's own information, different theme, and uses different modules. The Single code base simply means that the Drupal files are up-loaded to the server One Time.
-The modules are all in the sites/all/modules directory.
-The themes are all in the sites/all/themes directory.

Set up the domains to point to the Drupal folder

This setup was very quick and easy using my web host control panel.
In my setup, Drupal is in a subfolder. my-web-host-root/drupal

The File Structure in the Drupal folder.

This just makes it much easier to keep things up to date.
All the modules and themes are available for all the sites to use.
my-web-host-root/drupal/sites/all/modules
my-web-host-root/drupal/sites/all/themes

Each site or domain has this same set of files

Folder structure for 'each' site (2 domain examples)

my-web-host-root/drupal/sites/davebeall.name
my-web-host-root/drupal/sites/davebeall.name/files
my-web-host-root/drupal/sites/davebeall.name/tmp
my-web-host-root/drupal/sites/davebeall.name/default.settings.php
my-web-host-root/drupal/sites/davebeall.name/settings.php

my-web-host-root/drupal/sites/davebeall.me
my-web-host-root/drupal/sites/davebeall.me/files
my-web-host-root/drupal/sites/davebeall.me/tmp
my-web-host-root/drupal/sites/davebeall.me/default.settings.php
my-web-host-root/drupal/sites/davebeall.me/settings.php

and so on for each site

The install process

Before configuring any sites, we need the database running.

Go to the root of the site and follow the install screens up to the create admin account and STOP there.

Install each site

Open your browser and goto the http:// first site.com and follow the install screens as normal.
During the install add a prefix to the database setup, but use the same original database.

Open your browser and goto the http:// second site.com and follow the install screens as normal.
During the install add a unique prefix to the database setup, but use the same original database.

Open your browser and goto the http:// third site.com and follow the install screens as normal.
During the install add a unique prefix to the database setup, but use the same original database.

Open your browser and goto the http:// ourth site.com and follow the install screens as normal.
During the install add a unique prefix to the database setup, but use the same original database.

Open your browser and goto the http:// fith site.com and follow the install screens as normal.
During the install add a unique prefix to the database setup, but use the same original database.

Open your browser and goto the http:// sixth site.com and follow the install screens as normal.
During the install add a unique prefix to the database setup, but use the same original database.

 I ran out of time at the moment to write-up more details, but it is on the TODO list...
Questions and comments are welcome, drupal.org/user/381695