rear speaker placement for new theater

I am planning a media room about 17 by 27, with the projection tv along one of the short walls and the seating area about 12 feet away. As this is new construction, where should I put the surround speakers? On the rear wall? In the ceiling, slightly behind the seating area? Use dipoles on the side walls? Finally, can in-wall speakers really handle the dynamic range of the new surround protocalls? They seem really expensive for a small speaker without a box, and I don't see how they could perform as well as a small speaker with a properly designed cabinet. Thanks for the feedback.
I highly recommend you buy as close to full-range speakers for the rear as possible. I use floor standing speakers, the same type as the front left/right speakers. This places the tweeter and drivers at the same relative height to your ear. Also, speakers that utilize the same tweeter and drivers will be timbre matched all the way around. Most people will quote you that bass is non-directional, and the subwoofer can do all the bass output for the entire system. But I have read several articles that state that bass is not entirely non-directional. The human ear can determine whether bass originates from the front or the rear. So sending the rear speakers as much bass as you can would be beneficial, especially since your room is 17x27. Anyway, others out there may have a different theory, so let your own ears decide. If you must put speakers in/on the walls for either space or cosmetic reasons, I recommend placing them on the rear wall. I've heard a system with dipole speakers on the side walls, and I felt a lack of sound behind the listening position. Perhaps better speakers would do a better job. In-wall speakers have not really impressed me all that much. They effectively are using the air volume inside the wall for bass response. The ones I've heard are slightly on the boomy side when it comes to bass. Hope this helps you out.
Be sure to check out the link below (copy and paste it to your browser). There are several helpful articles there on home theater setup. In particular, you'll want to check out the article entitled, Face Off: Surround-Speaker-Configuration Wars. In a nutshell they found that 6.1 home theater sounded best when they used two "back" speakers. As I recall, the consensus was that the best setup used two dipolar back speakers and two monopolar side speakers, but it's been a little while since I've read the article. Good luck with the new system.
One more thing--I've yet to hear of an in-wall speaker that can match the performance of the better "box" speakers. If decor considerations require them, that's one thing. But if sonic performance is your objective, I wouldn't consider them. Just my $.02
I certainly agree with Argent: near rear wall and full range. In walls definitely compromise the sound. As for timber matching it is not as critical as the front three speakers, but there is no question that sticking to one brand will help create a seamless envelopment. I did say near the rear wall. I like the rear speakers about 45 degrees off from the central listening position. Now, I would recommend since this is a new construction that you wire for 8.1 surround. That means dipoles to the side and one central rear speaker. Who knows if this will ever be used--I find 5.1 channels is plenty to create a very satisfying theater experience--but as hardware and software progress there could be more channels. So even if you aren't going to hook up more speakers--wire it--it's cheap and if you ever decide to add speakers you'll be glad you did.