There are three editions of MS CRM 4.0

• Microsoft Dynamics CRM 4.0 Workgroup Server -> We can add maximum of five user if we are using workgroup server with single organization that can be installed on a single server.
• Microsoft Dynamics CRM 4.0 Professional Server -> It allows unlimited users with the ability to install  MS CRM Web server to be installed on multiple computers but with a single organization.
• Microsoft Dynamics CRM 4.0 Enterprise Server -> It Allows unlimited users and an unlimited number of organizations. Allows you to create role-based server instances, increasing scalability.