Автор: http://www.swissdelphicenter.ch

uses
  ComObj;

function OpenConnection(ConnectionString: AnsiString): Integer;
var
  ADODBConnection: OleVariant;
begin
  ADODBConnection := CreateOleObject('ADODB.Connection');
  ADODBConnection.CursorLocation := 3; // User client
  ADODBConnection.ConnectionString := ConnectionString;
  Result := 0;
  try
    ADODBConnection.Open;
  except
    Result := -1;
  end;
end;

function DataBaseConnection_Test(bMessage: Boolean): AnsiString;
var
  asTimeout, asUserName, asPassword, asDataSource, ConnectionString: AnsiString;
  iReturn: Integer;
  OldCursor: TCursor;
begin
  OldCursor := Screen.Cursor;
  Screen.Cursor := crHourGlass;
  asTimeout := '150';
  asUserName := 'NT_Server';
  asPassword := 'SA';
  asDataSource := 'SQL Server - My DataBase';

  ConnectionString := 'Data Source = ' + asDataSource +
    'User ID = ' + asUserName +
    'Password = ' + asPassword +
    'Mode = Read|Write;Connect Timeout = ' + asTimeout;
  try
    iReturn := OpenConnection(ConnectionString);

    if (bMessage) then
    begin
      if (iReturn = 0) then
        Application.MessageBox('Connection OK!', 'Information', MB_OK)
      else if (iReturn = -1) then
        Application.MessageBox('Connection Error!', 'Error', MB_ICONERROR +
          MB_OK);
    end;

    if (iReturn = 0) then
      Result := ConnectionString
    else if (iReturn = -1) then
      Result := '';
  finally
    Screen.Cursor := OldCursor;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  DataBaseConnection_Test(True);
end;