Okay, I'm just gonna compile this to one thread on its own as I'm driving myself bonkers trying to fix this.
I am wanting to install MAS to my subdomain, messengers.godspack.com.  I am using Godaddy and paying for my hosting.  Database is setup, install SEEMS to go fine.
Here's my config file:
<?php
//Mysidia Adoptables Site Configuration File
define('DBHOST', 'messengersadopt.db.12382978.hostedresource.com');             //DB Hostname
define('DBUSER', 'messengersadopt');             //DB Username
define('DBPASS', '****!');             //DB Password
define('DBNAME', 'messengersadopt');             //Your database name
define('DOMAIN', 'godspack.com');             //Your domain name (No http, www or . )
define('SCRIPTPATH', '/messengers');     //The folder you installed this script in
define('PREFIX', 'adopts_');
?>
This is what the site looks like when accessed through messengers.godspack.com:  
(image)
-Looks wrong but has correct URL
-I can't log in here, it just loops back to messengers.godspack.com/login and never actually logs in.
And this is what it looks like when accessed through godspack.com/messengers (which is where the directory for the subdomain is):  
(image)
-Looks right but has wrong URL
-Can't log in here either, as it just redirects to a 404 page with the url of godspack.com/messengers/login
I was up until 3am trying to fix this but no combination of different specificed domains and paths seems to produce the correct results.