Any help would be appreciated with this. I have been running Joomla 1.5.20 for a while now, and have a request for multiple sites to be configured that operate under the same server. I have downloaded the Multi Site and installed it. However, when I originally created the first (Master) site, all the DB was created using default jos_ format for the tables.

So my question is this:
1) I have purchased 2 new domains, how should i configure each domain in Site Manager?

a) I don't need to share users (actually I am preferring to manage users separately)

b) Currently symbolic linking is disabled (from what I read that shouldn't matter unless sharing DB/Ext/Mod/Plugins)

Any insights would be appreciated.

FYI, just checked and:
Unix Symbolic Links: Allowed
MySQL Version: 5.0.83-log Sharing supported

1) YES.
If you have purchased 2 domains, you have setup them in your HTTP Admin tool (ie. cpanel) and you have to defined them into JMS Multisites - "Manage Site" menu.
b) Symbolic Link is used for the files and folder (This is not related to the DB).
So if you want to be able have a specific deployed directory for your new 2 domains then you must have the Symbolic Link allowed to provide the full path directory where you want that the domains have their directories.

See for example the tutorial video CP-04 that show something similar for a subdomain a cPanel.
If you are using cPanel, you must create an AddOn Domain where you will specfy the document root that must be equal to JMS Multisites "deployed directory". Same location in both HTTP Admin tool (ie. cpanel) and JMS Multisties deployed directory.

I suggest that you have a look in the different tutorial video that may help you understand the concept and also understand how works the symbolic link.
www.jms2win.com/tutorial

ok, that seems to work well.

Now, I suppose if I want to copy some of the templates over I will have to follow the directions you give in This VIDEO (www.jms2win.com/tutorial#jms12x-CP-05), correct?

That would allow me to then utilize existing templates and then modify them without changing my existing master site - correct?