NAV implementation related cost on micro business

SBS CAL encompasses the user CALs for Windows Server, Exchange Server and SQL Server
source

MSDE limitations

SQL Server 2000's Enterprise Manager (as well as later versions such asSQL Server Management Studio) can be used to connect to [MSDE]
source

Navision SQL Option and MSDE
- very old thread

SQL 2000 Personal limitation:
performance degrades when more than five Transact-SQL batches are executed concurrently
source: Choosing an Edition of SQL Server 2000 (choosed.doc)

The Personal Edition is probably the most confusing SQL Server version because you can't buy it. According to the End User License Agreement (EULA), the Personal Edition is part of the Client Access License (CAL) and client software. If you have Standard or Enterprise Edition licenses, you get Personal Edition for free, but you can't buy it as a separate product.
source: SQL Server Version Differences