[support] Multiple Drupal Sites Errors

[lists at southernohio.net]

I'm trying to set up the following scenario:
mydomain.com/main is the primary Drupal installation.

I am wanting users to be able to access a new Drupal site at:
mydomain.com/main/NewSite

In order to accomplish this, I have the following already in place  
(I'm on a linux server with plesk):
~/httpdocs/main/sites/default/settings.php
~/httpdocs/main/sites/mydomain.com.main.NewSite/settings.php

I set the files in ~/httpdocs/main/sites/mydomain.com.main.NewSite/ 
settings.php up to the new database for that site, however each time  
I go to "www.mydomain.com/main/NewSite" I get the default Drupal site  
error: "Page not found"

I've been pouring over documentation I can find on multiple sites on  
one Drupal install, but am not having any luck.  Could someone please  
offer some suggestions or help to ascertain what might be going wrong  
here?

Thanks so much.

-George