Not exactly the best room shape for a "theater". Also, if you are using a satelite speaker setup i wouldn't be concerned with sound proofing. The wall is plenty big for a 36" TV.
Follow the other guys advice and hire a pro to do this for you. You will be much happier in the end. If you figure the cost of building a new house, spending 5% of that for this room will get you something a hell of a lot better.