Grand Am Major Problem?

Ok, so I bought this car in September of last year from a friend for $500. When I bought it, there was a problem with the pipe leading to the muffler where it had rusted, so I had it fixed for $80 and the car was extra quiet after that. Except for when I would turn it on and the alternator belt would squeal like a pig. I had it replaced, twice, and now it doesn't squeal. Yay? Now whenever it rains, I can hear the belt slip from time to time while I'm driving and whenever I accelerate the car sputters and stalls and makes a clapping sound in the engine. It did it today while I was going to school and doing about 55, I turned into a church parking lot and the battery light came on and the power steering seemed to shut off as I had a hard time turning. I turned around and decided to skip school so I wouldn't be stranded 20 miles from home and drove back to my house. On the way home I turned off my head lights and left the parking lights on, had the windshield wipers on low, and had the stereo on, but no heat because whenever I run the headlights and heat that seemed to make it run rough. So I get home and park it and the car is running worse than usual and whenever I rev the car in park the muffler pops. Could this car be nearing its 500 dollar limit?

Update: I just went outside and turned the car on again and turned everything on, even the headlights on high beam and the engine was shaking bad. I opened the hood and I saw that the engine was shaking back and forth almost violently. Could it be the spark plugs/wires?

First of all what size engine and what year is the vehicle? The problem you are having is probably related to a lack of voltage to properly fire the ignition system. To repair the vehicle you need to get a new tensioner and a new belt. The battery will need recharged and the alternator should then be able to maintain the battery. The new belt should also cure the power steering problem.