Hi,
My office has a layout that I need to change as I feel that’s improper and inefficient.

Current layout of office (workstations run windows-2000-pro):

There are 80 workstations available (in the same premise) across 4-LANs that are disconnected from each other. 4 LANs belong to 4 different business clients. In order to impose security policy so that they are unable to share data the idea of disconnected LANs was implemented.
(1) LAN-1, LAN-2, LAN-3 have 20 workstations each arranged in Workgroup and are peer-to-peer.
(2) LAN-4 has 20 computers (19-workstations & 1-Win2k-Advanced-Server). The server runs as a Domain Controller (DHCP-server). The users here login with their username-password and domain-name “XYZ” and start using their resources.

What I wish to do:

I wish to have only one single LAN with 79Workstations and 1 Server (Domain Controller, DHCP server). I wish to separate our 4 business clients logically (not by disconnected LAN). I want to make sure that security policy is equally implemented and data sharing is restricted within business and not beyond.

Any help is highly appreciated.

Regards,
Prodigy