do you mean your alternator belt or timing belt,hope its alternator,maybe get a better response if you state age,engine size,power steering,aircon etc as the belts are different sizes and route differently T:
If you do mean the drivebelt for the alternator and waterpump on the 1.9d engine then its an easy one to replace but you will have to remove the power steering belt to get it on,the route goes from the crank to the alternator then below the waterpump pulley and back onto the crank.The waterpump pulley doesnt have grooves for the grooved belt to run in like the waterpump and crank pully's.
You know this engine is interference type right? If your drive belt (cam belt) snaps it generally leads to valves and pistons connecting. Probably won't help to just put a new belt on before you check for damge. Did it make a lot of noise before it stopped etc?