一般我们能过VS2005的SQL explorer来添加一个本地的MDF文件。也许你可能会出现下面这个问题：
Exception Details: System.Data.SqlClient.SqlException: The user instance login flag is not supported on this version of SQL Server. The connection will be closed.

通过搜索。发现这里有我们所需要的信息：Error Message: The user instance login flag is not supported on this version of SQL Server. The connection will be closed

仔细分析Scott的回答：

"The issue is that User Instancing, which allows the automatic creation of databases from code, isn't support on the full version of SQL 2005.  That is a function of SQL Express only.  The solution is to manually create the database in SQL Server 2005 and set a connection string to point to it.  You will also need to run aspnet_regsql.exe manually against the database if you will be using any of the new built-in database features of ASP.NET v2.0."

因此，如果我们不是使用的从MS下载下来的SQL Server 2005 Express，那么我们只能过过在SQL2005管理器上把MDF文件添加进去在连接它。

解决方法：在SQL2005管理器上，通过Attach（附加）本地的MDF文件成功之后。在VS2005的sql explorer的连接即可。

以后继续补充。