[[duilioisola]]

Aquí tienes el código del que te hablé antes.
Pon un TMemo llamado Memo1 alineado alTop y deja un espacio abajo para que aparezcan los dos paneles.

Código Delphi [-]
unit UPruebaDragAndDrop;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ShellApi, StdCtrls, ExtCtrls;

type
  TPanelDragAndDrop = class(TCustomPanel)
  private
    FFiles : TStrings;
    OriginalPanelWindowProc : TWndMethod;
    FOnFileDrop : TNotifyEvent;
    procedure PanelWindowProc (var Msg : TMessage);
    procedure PanelFilesDrop (var Msg : TWMDROPFILES);
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  published
    property OnFileDrop : TNotifyEvent read FOnFileDrop write FOnFileDrop;
    property Files : TStrings read FFiles write FFiles;
  end;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    procedure PanelFileDrop(Sender: TObject);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

/// ********** ********** ********** ********** ********** **********
/// TPanelDragAndDrop
/// ********** ********** ********** ********** ********** **********
/// Descendiente de TCustomPanel
/// Acepta que le hechen archivos
/// Publica un evento OnFileDrop
/// Publica la lista de archivos que le cayeron
/// NO VACIA LA LISTA DE ARCHIVOS

procedure TPanelDragAndDrop.PanelWindowProc(var Msg: TMessage);
begin
  if Msg.Msg = WM_DROPFILES then
    PanelFilesDrop(TWMDROPFILES(Msg))
  else
    OriginalPanelWindowProc(Msg);
end;

procedure TPanelDragAndDrop.PanelFilesDrop(var Msg: TWMDROPFILES);
const
  MAXFILENAME = 255;
var
  cnt, FileCount : integer;
  FileName : array [0..MAXFILENAME] of char;
begin
  FileCount := DragQueryFile(msg.Drop, $FFFFFFFF, FileName, MAXFILENAME);
  for cnt := 0 to -1 + FileCount do
  begin
     DragQueryFile(msg.Drop, cnt, FileName, MAXFILENAME);
     FFiles.Add(FileName);
  end;
  DragFinish(msg.Drop);

  if Assigned(OnFileDrop) then
     OnFileDrop(Self);
end;

constructor TPanelDragAndDrop.Create(AOwner: TComponent);
begin
  inherited;
  FFiles := TStringList.Create;
  Self.Parent := TWinControl(AOwner);
  
  OriginalPanelWindowProc := WindowProc;
  WindowProc := PanelWindowProc;
  DragAcceptFiles(Handle, True);
end;

destructor TPanelDragAndDrop.Destroy;
begin
  FFiles.Free;
  inherited;
end;

/// ********** ********** ********** ********** ********** **********
/// TForm1
/// ********** ********** ********** ********** ********** **********

procedure TForm1.FormCreate(Sender: TObject);
var
  i : integer;
  Panel : TPanelDragAndDrop;
begin
  //Creo el panel1
  Panel := TPanelDragAndDrop.Create(Self);
  Panel.Parent := Self;
  Panel.Name := 'autoPanel1';
  Panel.Align := alLeft;
  Panel.Show;

  //Creo el panel2
  Panel := TPanelDragAndDrop.Create(Self);
  Panel.Parent := Self;
  Panel.Name := 'autoPanel2';
  Panel.Align := alRight;
  Panel.Show;

  for i := 0 to ComponentCount-1 do
  begin
    if (Components[i] is TPanelDragAndDrop) then
        (Components[i] as TPanelDragAndDrop).OnFileDrop := PanelFileDrop;
  end;
end;

procedure TForm1.PanelFileDrop(Sender: TObject);
var
   i : integer;
begin
  Memo1.Lines.Clear;
  Memo1.Lines.Add(Format('Entraron %d archivos desde el panel %s', [TPanelDragAndDrop(Sender).Files.Count, TPanelDragAndDrop(Sender).Name]));
  for i := 0 to TPanelDragAndDrop(Sender).Files.Count -1 do
  begin
     Memo1.Lines.Add(TPanelDragAndDrop(Sender).Files[i]);
  end;
  TPanelDragAndDrop(Sender).Files.Clear;
end;

end.