I would say that your belt is not the problem. I would bet that you have a bad pulley, and it is a bearing squeaking.
FWIW, I would stay away from the belt dressing stuff. Often times, this can cause a belt to slip, and while the squeaking goes away, it will wear your belt out faster. The belt dressing stuff is not your friend.
I would suggest pulling off your belt, and spinning each pulley by hand. The idler and tensioner pulleys should spin freely, and continue to spin for only a couple seconds. If the pulley stops spinning right when you let go of it, if it makes a squeaking noise when you spin it, or if it seems like the pulley wants to spin forever, I would suggest replacing it with a new, metal one.
But unless the belt has a lot of cracks, or sections missing from it, there is no need to replace it.
