I should have checked this out first, and I thought I had. Everything I had read said you can license Photoshop across platforms. I called Adobe today to do just that, and found out otherwise. Sure, they'll license across platforms if you're switching from one to another. But they demand monogamy. You can't have the same activation on both a PC and a Mac.
So far my other programs--Photo Mechanic, Eye One--are loading just fine. I oughta read something on this, because installing a program is way different from what I'm used to. Basically, it seems like nothing has happened. There's no desktop icon (except some file you have to throw away--what's that about?) and nothing conclusive about the process. After the download I had no indication that Photoshop was already on my system, because I couldn't find it, until I reinstalled over it. And then it's a manual procedure to drag it over to that Dock thingy, so that it's possible to someday find it again.
I hope all you Mac users are amused by the observations of an alien in your culture. I am not, repeat, not bashing anything here. I'm just documenting my awkward baby steps.