Authentication

We have a W2K network with AD installed. We have multiple offices in SA. Our main office is in JHB. I am currently in PTA. When users log onto the network, they authenticate to different domain controllers through out the country. We have one GlobalCatalogue server which is located in JHB. We do have other offices internationally. Each country has one main office. How do we get users to authenticate to there local servers? Each country is setup as a site, what I suggested is that each branch office be setup as a site but that does not follow our IT policy.