I dont know of a forum/messageboard, but cant say I have looked, I have done my own research on line. My mother is in the fairly advanced stages of Alzheimers.
From our experience, research, speaking to other people in same position, I would say to check what medication your parent is taking, as we have found that since stopping all medication the progression of the disease has slowed down dramatically. We have been through the aggressive stage, shouting, walking about non stop, scratching parts of the body and rubbing the hair until she has bald spots. She is now totally self reliant on care, incontinent, cannot feed herself etc, but has been in the same 'state' for a few years now without getting any worse.
Having had the disease for nearly 15 years now, and having been on a lot of drug trials (together with chinese herbal medicine) we found that a lot of the medication given to people with dementia and alzheimers is for schizophrenics and actually causes a lot of the side effects as mentioned above, and since we stopped giving her them she is much easier to care for.
Hope this helps.