Microsoft SQL Server 2005 hotfixes are created for specific SQL Server service packs. You must apply a SQL Server 2005 Service Pack 2 (SP2) hotfix to an installation of SQL Server 2005 SP2. By default, any hotfix that is provided in a SQL Server service pack is included in the next SQL Server service pack.
The cumulative update package 2 for SQL Server 2005 SP2 contains the SQL Server 2005 hotfixes that have been released since the release of SQL Server 2005 SP2 occurred.
The article continues at http://support.microsoft.com/kb/936305