Kat,
My dad had the same symptoms your say your dad is having. We were told he has a stroke and that is why he had short term memory loss. We all thought it was the start of Alzheimer's. My mom refused to believe it, and kept taking him to different doctors and finally about two years ago, he was diagnosed with NPH (Normal Pressure Hydracepalus (sp?), anyway June of 2006 he had surgery, they inserted a shunt and drain, and the improvement is amazing. He used to repeat himself all the time, he could not follow a conversation, and he told the same story at least 10 times. He couldn't remember he ate, so he ate again. He also couldn't remember who the new grandchildren and great grandchildren were. It was crazy, sad.
Since the operation his memory has returned about 50%. By June of this year they expect him to have 90% of his memory back. He can remember everything going on now during the day and what happened yesterday, he knows the new grandchildren by name. When he gets really tired, he has some trouble remembering, but i can't tell you how GREAT he is doing now. The difference is amazing. Even in the hospital right after surgery, the confused look was gone and he looked clearer and more alert.
I never worried that he might have an AN, because I read they are not heriditary. I hope your father's cat scan is clear of AN and they can diagnose and provide a treatment alternatives for him.
Good luck to you, your father and your family,
Denise