Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

procedure ShowContents(Value: Boolean);
 begin
   SystemParametersInfo(SPI_SETDRAGFULLWINDOWS, Ord(Value), nil, 0);
 end;

 // To Show window contents while dragging: 

procedure TForm1.Button1Click(Sender: TObject);
 begin
   ShowContents(True);
 end;

 // To disable this option call the function: 

procedure TForm1.Button1Click(Sender: TObject);
 begin
   ShowContents(False);
 end;