Holy Smokes! -- LoudspeakerMusic, you deserve to give yourself a new set of fabulous speakers!
I CONFIRM that your 'work around,' method worked. I set up a second Administrator account, as you indicated, and Presto! Age of Empire 2 was installed, up and running.
I logged out, logged in, checked it again. It works fine.
ALSO -- I was able to do this with an important data program I had/have for a Palm Pilot. That program also would not install and I was emailing the company and phoning them, 'cause it contains Five Years of names, addresses, phone numbers, birthdays, shopping list, Everything -- and Palm was telling me: "too bad, we're sorry."
So, this is a Great Discovery you made. Nice work. Thanks.