Windows 2003 Active Design

Clarifications

you will be better off opening a book and read through as what you asking can fill pages.
The best advice I can give you is before you do anything draw a logic chart of how each location organize according to you business specification from there you can start set up global security groups.
Develop your GPO's for those groups depends on permissions you want to assign to users in specific groups, and assign users & computers to them.
Once that done on each location you can then start planing universal groups if you need too.
As for DNS again the best advice I can give you is that there will probably be 1 main DNS address your domain address such as interswift.com, then subnets appended to this but again it all depends on your initial design of the forest\s.
As you can see I can go on and on...
So open win2003 server MCSE book or AD book and have a read.

Im surprise at the question.

Sorry to say but you the IT guy do not design an AD environment.

As animatech suggested, I would suggest you read a MCSE or AD book. Then you'll see why animatech and myself suggest you read about designing an AD environment. Then you'll see you the IT guy doesn't design it.