The unofficially redistributed official Apple Bootcamp USB drivers didn't seem to do anything for my new Apple Magic Keyboard.
winkbdlayouts provided me a UK Apple layout. It's not perfect (tilde and backtick are swapped, for one thing), but it does get most keys. Initially, it didn't seem to have installed properly, so I ended up editing the registry keys to remap the default UK keyboard to the Apple one, but later I found that I'd simply needed to restart the computer to re-read the registry keys.
Update: I actually find no difference between the custom United Kingdom Apple (WKL)
layout and the ready-installed English (United Kingdom)
layout. Waste of time.
I didn't end up buying kbdedit, but it helped me understand the layout of things.
Another thing to try would've been Magic Utilities.
Here's the "before" state of the registry before I changed it. I found out that this hack wasn't necessary anyway, however.

Here are the values I learned from winkbdlayouts:
