R – Will embedded Firebird/Delphi cause a firewall ‘hit’

To use the FastMM included with D2007, use SimpleShareMem as the 1st unit in both your application and the DLL projects.

Or download the full FastMM4 from SourceForge, set the Flags in FastMM4Options.Inc (ShareMM, ShareMMIfLibrary, AttemptToUseSharedMM) and put FastMM4 as the 1st unit in both the application and the DLL projects.

Embedded can't be used by multiple users at the same time (even if it's two applications on the same machine). See here for information on the differences between the three versions. There's also information in another SO question that might help.

As far as specifying a server at runtime, this may help:

procedure TForm1.Button1Click(Sender: TObject);
var 
 Conn: TSQLConnection;
begin
  Conn := TSQLConnection.Create(Self);
  try
    Conn.DriverName := 'FirebirdConnection';
    Conn.Params.Add('User_Name=SYSDBA');
    Conn.Params.Add('Password=masterkey');

    // Replace the dbname in the next line with the
    // value obtained at runtime, as  in
    // Conn.Params.Add('Database=' + YourNewPathAndDBName);
    Conn.Params.Add('Database=C:\FireBirdData\YourDB.fdb');

    Conn.Open;
    if Conn.Connected then
      ShowMessage('Connection successfully made to DB');
  finally
    Conn.Free;
  end;
end;