So the XP computer is pretty bad and wouldn't run SFCOP.
So I had to install SFCOP, copy it over to my computer, then register the serial number.
Then I had to run the patch on the XP computer, and copy the patched SFCOP over to my computer, and overwrite the registered version, and when I started it, no need to reenter the serial # (which I think can't be entered on a patched install anyway?).
This actually worked.
I feel like I'm making this more complex than it needs to be, but it's working so yay.