In any casserole type dish with the exception of lasagna, you'll need to cook the pasta under al dente. There should be more of firmness when you bite down on the pasta before you add it, since it will continue to cook and soak up liquid in the casserole. Some lasagnas you can add dry without boiling them first. Those will specify on the box whether you can or not.
Regarding cooking pasta in the microwave, I wouldn't do it. You won't be able to consistently get good pasta. A pot of boiling water is the best way. It wouldn't make sense to sacrifice texture and quality just to save on a few minutes.
