I think that if you've got a dedicated ht room with those dimensions, you should really go front projection. Don't know where Razz1234 got his information, but for a rough estimate of viewing distance go here:
http://www.myhometheater.homestead.c...alculator.html
It says you can sit about 11 or 12 feet away from a 100" screen, so 30 ft. should be plenty!!
You also don't need to spend 5 grand on a projector, a lot of people seem very happy with the new LCD's such as the Benq's, for like $1200. You can even make your own screen if you want. They are much quieter, smaller, and lighter than the old style monster CRT projectors (which however, are still considered the best PQ)
They do have a limited bulb life, but replacement is under $500, and should last 3-6 yrs. under normal usage.