Vineet, Buffing and and polishing will do the trick for you. Scratches in windshield can often be buffed off just as in the painted surface. There are lot of glass scratch removal products available in the market. If the scratches are small, then you can buff it using hand. But if the scratches are prominent, then you have to get it to the experts and get it done using a good buffing machine and then do a polish. From what I have found , you can get if rectified from www.windshieldexperts.com in India. I feel you need not replace the windshield. Buffing and polishing will be enough. Also as suggested by sgiitk, get your wiper blades replaced at regular intervals or as you see wear and tear in the rubber. Normally people staying in apartments have the habit of giving the car for daily wash to the car washing guys. These scratches are sometimes caused by them as they use the same towels for 20-30 cars.