Gosh, Terence, if I knew that I needed to make a purchase, I'd not be posing a question here. I did already make a purchase, though it may not have been the correct one.
Before you read on, by all means, let me know what I need to purchase. I say that because the rest of my post is partly a rant, though a reasoned one.
So I've worked this issue both backwards and forwards. I bought the latest version of iPhoto, version 9.4.1. But when I booted it, i was told that I needed version 9.x.x. The older version kept asking for the next oldest version. OK. So I went the other way. I started with my own version: 8.1.2. I added updates 'til I arrived at this impasse: both the 8 series needed the very first 9 series and the oldest 9 series needed the very first 9 series. That version, acc to Apple, is called version 9.0.1. It doesn't exist on Apple's update/upload pages. I used Google to find a discussion of it. Great! Not only did I find a discussion, the writer was kind enough to hotlink "9.0.1" to the web page on which it, supposedly, was available. No such luck: Both times I tried, I got the same Apple page which did not offer 9.0.1, but only 9.1.
The goal: use iPhoto and Preview to edit my RAW files. I have downloaded the (free) latest update to do so. Now all I have to do is to get iPhoto (and Preview) to work.
If, when starting from 8.1.2, a purchase was needed, it sure would have been great had Apple made a note of it. If there was no way to get from 8.x.x to 9.x.x without a purchase, it sure would have been great had Apple made a note of it somewhere.