I agree with Dolly, if you don't have very good technique in Pilates you can do more harm than good, specifically to your back. There are certains things you need to do in order to make the excercises safe and effective and I don't think you would be able to do that without being able to see it really.
It's just my opinion but I would always encourage people to go to a class if they are starting off, for yoga or pilates, as there are a lot of little things that can make a big difference to your practice. Simple things like having your pelvis tilted the correct way can mean the difference between an effective pilates workout and a very sore back.