Different projectors have different throw ratios. The throw ratio is the relationship between your projectors distance from your screen and the width of the image.
All my projector installations were done by Big Daddy A/V Installation Company.
My screen is a Da-Lite permanet wall mount white screen with a diagonal width of 120". It is installed permanently on the wall. My Epson 1080UB projector is installed about 12-13 ft away from the front wall and about 7ft-8ft away from the rear wall. The picture is really good. Of course, the zoom lenses on the projectors give you some flexibility in installation.
I don't believe you need a special beam. The normal beams and studs should be able to carry the weight. I cut a 2 x 2 piece of high quality plywood and attached it to the ceiling with the help of a stud finder that I bought from Home Depot. I then used a standard projector bracket to install the projector to the plywood. You can use any color you like to paint the plywood.
For electrical wiring, I hired an electrical contracter that was cheap and had him install two 20 amp plugs on the wall and a plug on the ceiling close to where I wanted to install the projector. He also installed two ceiling fans out of the way of the projector.
These sites may be helpful:
http://www.presentersonline.com/tech...distance.shtml
Viewing Distance Calculator:
http://hometheater.about.com/gi/dyna...alculator.html