I have a small environment (60-65 users though we were up to 130 a few years
ago). Our tree is a holdover from NetWare 4.0 and has few major changes. I
need to implement DSfW and I’m confused about the existing tree and where
I should place it. My DNS domain is "mhtn.com" and I would like to not have
a separate domain for DSfW. Here is a facsimile of my tree. I run OES2
sp3 currently with plans to migrate to OES 11 and possibly virtualize a
great deal of what I have.

+Root/MHTN_TREE
|
+-+ MHTN
|
+-+ SLC
|
+-+ Extend
|
+-+ Servers
| |
| +New Server Objects
+- Group Objects
+- User Objects
+- Old-Server-Objects
+- GroupWise system
+- DNS/DHCP locators and containers

My questions are:

Where do I place DSfW in my tree to have minimal impact on the existing tree
structure?
What changes do I need to make to my tree to accommodate DSfW?
What is the correlation between the Internet Domain name and the DSfW domain
name?