Here's an object that enables you to move your objects on a form easily during runtime...

  TObjectMover = class(TObject)
  Private
    { Private declarations }
    MousePosInfo  : TPoint;
    CurrentObject : TControl;
    WindowHandle  : THandle;
    fSnapGrid     : Integer;

    Procedure WndProc(var Msg: TMessage);
  Protected
    { Protected declarations }
  Public
    { Public declarations }
    Constructor Create;
    Destructor Destroy; override;

    Function BeginMove(Obj: TControl) : Boolean;
  Published
    { Published declarations }
    Property SnapGrid : Integer read fSnapGrid write fSnapGrid;
  End;


Constructor TObjectMover.Create;
Begin
   Inherited Create;

   WindowHandle := AllocateHwnd(WndProc);

   fSnapGrid     := 8;
   MousePosInfo  := Point(0, 0);
   CurrentObject := NIL;
End;

Destructor TObjectMover.Destroy;
Begin
   DeallocateHwnd(WindowHandle);

   Inherited Destroy;
End;

Function TObjectMover.BeginMove(Obj: TControl) : Boolean;
Begin
   Result := False;

   IF (Assigned(Obj)) Then
   Begin
      IF (Assigned(Obj.Parent)) Then
      Begin
         Result := True;

         CurrentObject := Obj;
         MousePosInfo := CurrentObject.ScreenToClient(Mouse.CursorPos);
         CurrentObject.BringToFront;
         SetCapture(WindowHandle);
      End;
   End;
End;

Procedure TObjectMover.WndProc(var Msg: TMessage);
Var
  P : TPoint;

Begin
   IF (Msg.Msg = WM_MouseMove) Then
   Begin
      IF (Assigned(CurrentObject)) Then
      Begin
         P := Mouse.CursorPos;
         P := CurrentObject.Parent.ScreenToClient(P);
         Dec(P.x, MousePosInfo.x);
         Dec(P.y, MousePosInfo.y);

         CurrentObject.Left := P.x - (P.x mod fSnapGrid);
         CurrentObject.Top := P.y - (P.y mod fSnapGrid);
      End;
   End;

   IF (Msg.Msg = WM_LBUTTONUP) Then
   Begin
      IF (Assigned(CurrentObject)) Then
      Begin
         CurrentObject := NIL;
         ReleaseCapture;
      End;
   End;
End;





To test the new object:

Procedure TForm1.FormCreate(Sender: TObject);
Begin
   ObjectMover := TObjectMover.Create;
End;

Procedure TForm1.FormDestroy(Sender: TObject);
Begin
   ObjectMover.Free;
End;

Procedure TForm1.ListBox1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
Begin
   IF (not ObjectMover.BeginMove(ListBox1)) Then ShowMessage('Failed to move object!');
End;