Windows for Small Business Server is the version of the Windows Server OS we use to build Windows Small Business Server 2003. We are making it available separately for customers who want to build a small business suite without Exchange.
It is $479US with 5 CALs. Incremental CALs are $79US each and are enforced, using the same technology as SBS. CALs are capped at 15, after which point it is cheaper to simply use Windows Server Standard Edition to build a small business suite.
It is not intended for general purpose use, rather to be used as the foundation for a small business suite solution. As such, there are limited management configuration tools since administration tasks would be solution-wide, not OS specific.
Like SBS, Windows for Small Business Server, is licensed and deployed as a domain controller at the root of the directory forest, trusts to other domains is disabled.