A friend of mine did that a few months ago once I convinced him to completely switch over (FCP > PPro on Mac > PPro on PC). He called sales directly and they took care of it. Can't say for sure that will be the policy in the months or years to come, though.
EDIT: Come to think of it, it may not be an issue when you're going from one version to another, e.g. CS5.5 to CSNext. Since even an upgrade is a standalone install, there are no platform prerequisites that I'm aware of; it's simply a matter of serial number. When my friend did the crossgrade, he was actually going from CS5 on the Mac to CS5 on the PC, so that was a true crossgrade. No matter what, call the sales folks (actually based in the US as far as I'm aware, unlike technical support) and they'll be able to give you the details; a reputable third-party vendor would probably have that information as well.
I'll probably want to upgrade the computer hardware to a windows machine
Thank You! It's great to have all these people switching from FCP to PP, but that's only half the process. We need more full conversions here, people.
Don't be afraid to switch Windows 7. Come back into the Light from the Mac side.
Thanks Todd and Colin!
Jim, I'm not really sugesting that PCs are better than Macs, just that when my MacPro gets old it will be old, and anything newer will be better. I'm pretty agnostic here having both PCs and Macs in the studio. I just want what is going to work best for the software.