@BigBlockin,
Considering that neither Plato or Aristotle could comprehend something like stem cell research it is hard to say how they would view this issue based on their beliefs. This is also the reason why Aristotle never prescribes a set of actions in his ethics and instead relies on character building.
Both would probably have no issue with the practice. Aristotle would say as long as the researcher does their function well then it would be fine. See Nicomachean Ethics if you want to get into Aristotle's ethics. Plato would take a more metaphysical approach, but would probably conclude that stem cell research when done properly aligns with the good.
This is one of those ethical debates that is hard to include Plato and Aristotle. Now Kant and John Stuart Mill on the other hand, would have a lot to say on the subject since this falls into the realm of both deontological and consequentialism ethics.