Maybe something like this (not tested):

Code:
var
  LastBonusScore : integer; //Set to zero when starting a new game

procedure TFormGame.BonusLife;
begin
  if (Points >= LastBonusScore+25000) then
  begin
    Inc(Lives,2);
    Inc(LastBonusScore,25000);
  end;
end;
It should give you a bonus every 25000 points.