Some suggestions:

• Is the SQL browser service running?
• Double check that you entered in the correct instance name in the SCSP installer
• Make sure that if you have already tried the install, there are not any residual users that have the letters "scsp" in the master Security > Logins folder in SQL Management Studio
• Make sure that in the SQL Server Configuration Manager, you have enabled "Shared Memory", "Named Pipes" and "TCP/IP" in the network protocols of the instance
• Make sure you create a unique instance for SCSP, this will avoid any conflicts with other instance settings required for other databases
• Ensure your password meets the SQL complexity rules (you can only use # and _ as non-alphanumeric characters for the SCSP users).  Or, as a less secure method to test the complexity issue, disable the password complexity rules for the instance in SQL Management Studio and see if that makes a difference.
• Make sure you are running the latest Service Pack of SQL.  See SCSP install guide/release notes for your version to make sure that you have at least the required SQL service pack level.

• SCSP is cluster unaware.  If you are using a SQL cluster, then SCSP sees it the same way it sees a single node install. Yes, you can install SCSP in a clustered SQL environment.
   
• Look for residual files in this location from a previous install:

  Manually delete all the files/folders in C:\Program Files (x86)\Common Files\Symantec Shared\SCSP\MSSQL.1\MSSQL\ directory before doing fresh SCSP server installation.
   

• What service pack of SQL 2k5 are you on?
   
• Look in the person who attempted the install temp directory (from command line, type %temp%) and locate the install log called SISManagementInstallWrapper.log.  Attach that file to this thread.
  Also look for log file here:

  - %ProgramFiles%\Symantec\Critical System Protection\Server\SISManagementInstallWrapper.txt

  - %ProgramFiles%\Symantec\Critical System Protection\Server\SISManagerSetup.txt

  - %ProgramFiles%\Symantec\Critical System Protection\Server\msde-dbStatus.txt

• Also open a command window and enter "net start" copy and paste the results into notepad and attach to this thread.
   
• Have you tried to connect to the instance using command line OSQL?  Note you will need SQL Client installed if you are using a remote machine to test this (recommended to ensure no firewall or network issues).  Note also that you will need an SA account that is active to do this:

OSQL –U sa –P <sa password> -S <hostname or IP address of SQL box>\SCSP (or database instance name used during the install)

You should get this prompt if this works:

>1

• Try connecting using both the IP address instead of the hostname, as a test for DNS issues.

To answer your MDAC question, that is the framework with which the SCSP installer communicates with the SQL server during the install process (setting up tables, users, stored procedures, etc).