The link below lists build numbers, KB numbers and links to cumulative updates updates 1 to 9 for SQL Server 2005:
List of build numbers and cumulative updates 1-9 for SQL Server 2005
Also see this post for relevance of SQL Updates to Microsoft Dynamics NAV:
Overview of updates for SQL Server 2005 SP2
Lars Lohndorf-Larsen
Microsoft Dynamics UK
Microsoft Customer Service and Support (CSS) EMEA