[Страдалецъ]

Ну тогда так:

Код:

procedure TForm1.StringGrid1MouseWheelDown(Sender: TObject;
  Shift: TShiftState; MousePos: TPoint; var Handled: Boolean);
begin
 StringGrid1.Perform(WM_VSCROLL, SB_PAGEDOWN, 0);
 Handled := True;
end;

procedure TForm1.StringGrid1MouseWheelUp(Sender: TObject;
  Shift: TShiftState; MousePos: TPoint; var Handled: Boolean);
begin
 StringGrid1.Perform(WM_VSCROLL, SB_PAGEUP, 0);
 Handled := True;
end;