Method 1
For 64 bit version, browse to System32 directory. For 32 bit, use SysWoW64 directory. Look for odbcad32.exe (ODBC Data Source Administrator). Double click on it and you can find the SQL Server Native Client version under the Drivers tab.
Method 2
Open the Registry Editor and go the following directory based on your Windows operating system.
SQL Server 2008 R2
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\SQLNCLI10\CurrentVersion
SQL Server 2008 / SQL Server Native Client 10
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\SQLNCLI10\CurrentVersion
SQL Server 2005 /SQL Server Native Client 9
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Native Client\CurrentVersion
SQL Server 2012
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\SQLNCLI11\CurrentVersion
