Well, i don't believe you need any prior training or any certain fitness level for yoga. The yoga program in my school is more or less a joke, as they do absolutly nothing and half the kids just lay on the mats and sleep. Given, the class size in my school is about 50 to a class, so theres not much cooperation and the teachers don't even care, so the students are allowed to do nothing. In your yoga program i would imagine you will be doing mainly steches, so beforehand you may want to stretch out for a week or so, just to make your body prepared for it. Again, I don't know about your yoga program, but if it's anything like my schools program, it's a joke.