procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
begin
  with (Sender as TListBox) do
    Items.Move(ItemIndex,ItemAtPos(Point(x,y),True));
end;

procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
begin
  Accept := (Sender=Source);
end;