[NumLock]

Код:

uses
  ShellAPI,

type
  TForm1 = class(TForm)
    ListBox1: TListBox;
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
    procedure ListBox1Click(Sender: TObject);

const
  PATH = 'c:\Program Files\Borland\Delphi7\';

procedure TForm1.FormCreate(Sender: TObject);
begin
  SendMessage(ListBox1.Handle, LB_DIR, 0, Integer(PChar(PATH+'*.txt')));
end;

procedure TForm1.ListBox1Click(Sender: TObject);
begin
  Memo1.Lines.LoadFromFile(PATH+ListBox1.Items[ListBox1.ItemIndex]);
  ShellExecute(0, 'open', PChar(PATH+ListBox1.Items[ListBox1.ItemIndex]), nil, nil, SW_SHOW);
end;

http://data.cod.ru/133824