The engine in my 96 saturn wagon shakes when it is put into gear, reverse or drive.

When i start my 96 saturn wagon the engine shakes a bit but when it is put into drive or reverse it starts to shake more violently. Also at that point when i shift it into gear the rpm's drop down to around 4 or 5 hundred rpm's causing to also want to stall out on top of the shaking. As if that wasnt enough i can hear a loud knocking coming from inside the engine. Lastly when the car is started and it is given gas while in gear the belt starts to scream deafeningly loud which from time to time causes it to melt the serpentine belt which then simply shreds into a rubbery spaghetti like state. Having to keep replacing the belts is becoming quite expensive at this point. Please help!!!!!