Q. What is Windows Server 2003 for Small Business Server?
A. Windows Server 2003 for Small Business Server is designed for partners who want to deliver a server solution based on Windows Server 2003 as part of their product offering. It provides the same version of Windows Server 2003 that is used by Windows Small Business Server 2003, but it has none of the added features included in the standard edition or premium edition of Windows Small Business Server 2003.
Windows Server 2003 for Small Business Server has the following restrictions:
• Only one computer in a domain can be running Windows Server 2003 for Small Business Server.
• Windows Server 2003 for Small Business Server must be the root of the Active Directory® forest.
• Windows Server 2003 for Small Business Server cannot trust any other domains.
• A Windows Server 2003 for Small Business Server domain cannot have any child domains.
• Each additional server must have a Windows Small Business Server 2003 client access license (CAL). You can use CALs for each user or for each device.
http://www.microsoft.com/windowsserver2003/sbs/techinfo/overview/generalfaq.mspx:-)