// In the PageControl's OnMouseDown event handler:  

procedure TForm1.PageControl1MouseDown(Sender: TObject;  
  Button: TMouseButton; Shift: TShiftState; X, Y: Integer);  
begin  
  PageControl1.BeginDrag(False);  
end;  


// In the PageControl's OnDragDrop event handler:  

procedure TForm1.PageControl1DragDrop(Sender, Source: TObject; X, Y: Integer);  
const  
  TCM_GETITEMRECT = $130A;  
var  
  i: Integer;  
  r: TRect;  
begin  
  if not (Sender is TPageControl) then Exit;  
  with PageControl1 do  
  begin  
    for i := 0 to PageCount - 1 do  
    begin  
      Perform(TCM_GETITEMRECT, i, lParam(@r));  
      if PtInRect(r, Point(X, Y)) then  
      begin  
        if i <> ActivePage.PageIndex then  
          ActivePage.PageIndex := i;  
        Exit;  
      end;  
    end;  
  end;  
end;  

// In the PageControl's OnDragOver event handler:  

procedure TForm1.PageControl1DragOver(Sender, Source: TObject; X,  
  Y: Integer; State: TDragState; var Accept: Boolean);  
begin  
  if Sender is TPageControl then  
    Accept := True;  
end;