The worse thing a person can do to their feet (and ultimately to their entire body) is to buy a pair of shoes that works against them.
If you are a supinator and buy a pair of shoes for an overpronator you will put serious stress on your arch and will give yourself a serious case of tendonitis in your lower legs.
If you are a pronator and buy a pair of shoes for a supinator, you will once again, put serious stress on your arch and will actually start hurting your knees, hips, and lower back.
Your best bet is to go to a specialty running shop, not footlocker or the finish line, and have a shoe specialist observe your running form and take a measurement of your foot. They can tell which way your natural tendency is to roll (in or out) and then make a recommendation for you. Many of them will do this service for free, charge you less for shoes, and actually provide you with service after the sale. They also tend to be locally owned, so you are supporting local businesses as well.
The last thing you want to do to your feet is to put them into the wrong shoes.