administartive and routing groups in Exchange 2000

here is the short of it from Swinc
http://www.swinc.com/resource/e2kfaq_sec2.htm
2.8 Q: How does an Exchange 5.5 site compare to an Exchange 2000 Routing Group or Administrative Group?

A: In a mixed mode Exchange environment the Exchange 2000 Administrative Group and Routing Group correspond to the Exchange 5.5 site. In a native Exchange 2000 environment, the Administrative Group is a group of Exchange objects sharing a common set of permissions and routing groups define how those servers communicate with one another. A single Administrative Group can contain several Routing Groups.

Example: Your north American Exchange servers might be grouped in a single Administrative Group, but subdivided into several Routing Groups to optimize interserver communication.

An Administrative Group contains zero or more Routing Groups.

Routing groups are pretty close to sites in exchange 5.5...