[0nni]

Код:

function EnumTaskWindows(wnd : HWND;ParentNod: TTreeNode): bool; stdcall;
var
  buff : array[0..256] of char;
  NewItem : TTreeNode;
begin
  ZeroMemory(@buff, sizeof(buff));
  GetClassName(wnd, buff, 256);

  NewItem := Form1.TreeView1.Items.AddChild(ParentNod, buff);

  GetWindowText(wnd, buff, 256);
  NewItem.Text := NewItem.Text + ' - ' + buff;

  EnumChildWindows(wnd, @EnumTaskWindows, Integer(NewItem));

  Result := true;
end;
begin
   EnumWindows(@EnumTaskWindows, 0);
end;

Добавь на форму TTreeView