Having followed through the process almost succesfully I should like to suggest an amendment/upgrade to the documentation. It might also identify where I have made whatever mistakes i have made

File names
In a situation where you have an existing file for a site http://www.mysite.com and you want to multisite http://www.myothersite into it you need to make a new directory to the /sites directory you will find within the mysite file system.
This directory should be called /sites/myothersite.com.
When you set up a new Drupal site you are asked for the database name, username, password and the prefix of files relevant to the site. This information has to be entered into Database Manager in http://www.mysite.com/admin/settings/multisite_manager and will generate a script
This script - which currently does not include the database password and omits the initial <?php - should be copied into a file called settings.php and pasted into the directory you set up above.
What Happens Next
Log into http://www.myothersite.com normally and the normal Drupa set up secreens will appear.
Complete this and then create the new site as if it were free standing.

These comments are hopefully useful to you.

Comments

schuyler1d’s picture

Thanks!

I put your content as a stub at:
http://drupal.org/node/427804

Please feel free to flesh this out further. I'm going to make this the main documentation link now.