A: Just put tnsnames.ora file in the same folder, where Oracle Instant Client is located. No need to do something other, like specifying TNS_Admin or TNS_Names. If you does not need to use TNS aliases, then put empty tnsnames.ora file. 

A: AnyDAC cannot initialize OCI in the Unicode mode, that is required for D2009. Most probably, that is due to the old Oracle client version. We will suggest:

• upgrade Oracle client software at least to v 9.0;
• or stay with a non-Unicode Delphi (<= D2007).

A: Using the following "roadmap" you can choose the correct Oracle client and Delphi versions:

• AnyDAC with Delphi 2009 or higher requires at least Oracle 8.1.5 client. Because only starting from Oracle 8.1.5 the client works correctly with Unicode.
• AnyDAC with Delphi 2007 or less requires at least Oracle 8.0.3 client.

A: Generic skeleton for your task may look like: 

ADConnection1.StartTransaction;
try
  ADConnection1.ExecSQL('LOCK TABLE ...');
  .........
  ADConnection1.Commit;
except
  ADConnection1.Rollback;
  raise;
end;

A: Use:

• TADPhysOracleDriverLink.GetOracleHomes – to get a list of known Oracle homes;
• TADPhysOracleDriverLink.GetTNSServices – to get a list of TNS aliases from the primary Oracle home.

A: Not at this moment. As a workaround you can build PL/SQL wrapping procedures and functions. Using this approach, you can then work with Oracle Advanced Queuing.