I have a grand am as well, '99, and unfortunately the factory stereo from my model and year does not support ipod functionality. Mostly because its so old. I'm working on getting a new stereo and depending on your year, you'll probably need a new stereo also if you want ipod compatibility.
Don't go some place like Wal-Mart trying to save money when it comes to something like this. That's okay for food or shampoo etc, but if you want good quality sound, go to some professional electronics store in your area or something a little bigger perhaps like BestBuy (I love their GeekSquad warranty + support they offer), and tell them exactly what you're looking for in a radio/stereo, what your budget is, and what they recommend.
Best of luck,
Kyle