Creating the DSN needed to connect vCenter 5.1 to SQL Server
Click Control Panel > Administrative Tools > Data Sources (ODBC).
Open ODBC connection, Select system DSN tab , then click on Add
Select native SQL client , click finish
It will ask for DSN name, enter name that you want for VC DSN.
Then enter VC database address.
Then it will ask for authentication, choose which option you want, like windows based or SQL based authentication.
Then click next and select the correct database that was created for VC from drop down option
Finish and test connection.