Regardless, I would start by getting copies of "Home Theater" and "Sound & Vision" magazines and take a look at what others have been doing and the equipment that they've been using for the type of room that you want. Then I'd take a look at who are the authorized retailers of the equipment that you think that you would want to use and go talk to them. Often, the specialty audio/video retailers either have their own in-house theater installers or they can recommend some contractors who specialize in home theater installs. Before choosing someone, ask for references and attempt to see some of the work that they've done.
I would also take a look at the AV Science Forum. They have forums for every type of equipment that you can imagine and 4 forums dedicated to different aspects of building a home theater.
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