On the third startup, the Win Dual-boot splash twirly never appeared, even after twenty minutes. So I powered off and on. It then displayed, "Preparing Automatic Repair," but did no such thing (automatic despair?). I decided that since this appeared to be a MBR-ish problem due to my trying to dual-boot, I might as well do what I was gonna do anyway, what normal people do. So I booted Gparted and reformatted the W10 partition, then used a Macrium Reflect boot to rebuild the MBR with no W10 stuff.
Then, like normal people, I booted my existing Win7, loaded my Win10 CD and chose its Startup icon. It then proceeded to install W10 within W7. There are plenty of differences, but nothing amazing or terrible, so far. It's more like everything acts the same but looks little different. It does seem to use a couple more megs of ram than before, despite claims to the contrary.
And, as predicted by Amoco, it says I really am still activated.
So far, so something...