The easiest way to attach the SplendidCRM to SQL Server is to use the SQL Server Management Studio.  In the studio, you right click on the Databases node of the object tree and select Attach.  Assuming that you have already copied the SplendidCRM.MDB and SplendidCRM.LDB files to the machine running SQL Server, the process should only take a few seconds.

Why do you need to attach the database?  Did you about the normal SplendidCRM install?

What is the reason you need to want to use the registry to define the database connection information?  While this is certainly possible, it is not common.  Your best bet is to remove the SplendidProvider appSetting from Web.confg and specify the full database connection string for the SplendidSQLServer appSetting.