Active Directory Design

We are in the design stage of deploying Win2K and Active Directory. We are in 8 states with multiply sites in each state. Some of the people on the design team want to setup a root domain with only 2 child domains under it and setup OU’s for all of the locations, while the others think we should have more child domains. Maybe in each state or support area. Can anyone help me out with the pros and cons to each of these plans. We have a apporx. 5000 users spread out over these areas. Security is an issue and the ones wanting to use the limited domain setup suggest it would be more secure.

All suggestion need.