How to match a version of SQL Server 2008? It is needed to install a new instance of SQL to the existing Windows SQL Server 2008. I have no idea what was used to originally install the existing 4 instances. Is it R5 SP32? Thanks to MS wonderful versioning system nobody knows just by looking at Add/Remove.

The version in Add/Remove is listed as 10.1.2531.0 for all the SQL components (funnily enough, all except the main "MS SQL Server 2008 (64-bit)". When I click "modify" under there it asks where is the original installation dir? I would be happy to know too.

How to find "just the right" installer, in order to avoid version hell, upgrading the existing instances (this is production) and other mess?
Version 10.1.2531.0 is for SQL Server 2008 Service Pack 1.
The following table lists the major releases of SQL Server 2008.


Release                         Product version

SQL Server 2008 Service Pack 3  10.00.5500.00
SQL Server 2008 Service Pack 2  10.00.4000.00
SQL Server 2008 Service Pack 1  10.00.2531.00
SQL Server 2008 RTM 10.00.1600.22


Check more details on SQL Server version

EDIT:

You can query database to get these info from database itself like


SELECT
 SERVERPROPERTY('ProductVersion') AS ProductVersion,
 SERVERPROPERTY('ProductLevel') AS ProductLevel,
 SERVERPROPERTY('Edition') AS Edition,
 SERVERPROPERTY('EngineEdition') AS EngineEdition;


More details on SERVERPROPERTY