I'm constantly switching between Mac and PC environments. I do it frequently enough that I make the usual mistake at the beginning - it's mostly undo. It takes about five mistakes and my brain rewires itself. No big deal.
That was, until I bought a DasKeyboard. Which is the best keyboard I've ever owned. It's based on the old IBM-M keyboard. Lots of 'clicky-clicky.' A day of typing with it...and my hands felt wonderful. It's just a pure joy to type with. I'm still not sure whether or not I should have bought the all black one. that's right, they have an all black keyboard with nothing on the keys. Part of me wished I had bought it - when you have no markings on the keyboard, you're forced to learn where the keys are. You become a better typist.
Back to the classroom; I get lots of switchers, or people forced to work off of their platform of choice. For whatever reason - no matter what sort of classroom I'm in (Mac or Windows), there's at least one person struggling with the switch. In fact, I have a posts here on how to remap the keyboard. For both Mac and PC.
I didn't really appreciate the problem that Cross Platform people really faced. What I do isn't the everyday use of a machine. Neither is the classroom. I bought this really great keyboard and the damn command and option keys were in the wrong place.
I had instant clarity over the frustration my students felt. I paid attention to my own (earlier) post about remapping, and i settled on KeyRemap4Macbook. And all was much much better. Now my uber cool Das Keyboard matched my internal keyboard.
It didn't solve my classroom problem, though. I still had students stumbling over this sort of muscle memory. Yes, I could install KeyRemap4Macbook. It even has a cool menu that permits easy switching back and forth. The only real issue was how do I teach other instructors (whom I work with) to deal with it. I wanted to be able to do this without third party software.
Turns out your mac could move the Command, Option, Control and Capslock keys. It's been able to do this since Tiger. And it keeps track of external keyboards separate from internal keyboard (perfect for buying the Das keyboard or any other non-mac keyboard for that matter.)
Here's what you need:

And then you need to adjust this as you like:

Now your student will grab CONTROL Z and it will completely undo. With less frustration. It works everywhere, is super easy to configure, and best of all...it's free.