Caine,
Thanks for this information. However, in looking in the registry for this information, it does vary based on the engine version. After 2000, there is an extra "Microsoft SQL Server" in the registry path. Also, the first "MSSQLSERVER" is the instance name, and being set to MSSQLSERVER means it will always look in the default instance for this information.
Wayne
Microsoft Certified Master: SQL Server 2008
Author - SQL Server T-SQL Recipes