I do the same thing Diane does, but I shrink the image down a bit so I can make the pop-up window smaller than the main window. The benefit to using this pop-up-answer-window approach is that the learner can compare the choices she made to the actual correct answers, since her original responses are still there. It also allows kinesthetic learners to go back to their answer and recreate what they're seeing as the correct answer, if they want to have that physical reinforcement.
