We have been providing a Windows beta version to customers who requested and have decided to go ahead and make it publicly available. The main functionality at this point is image capture, live view, touch and incremental focusing, property changes, image transfer and viewing, and focus stacking. The Windows version officially gets tested on Windows 7 and Windows 8. I would imaging it would work with XP, but we don't have a definitive answer at this time.
I would also like to point out the different between Windows 8 Pro (or just "regular" Windows 8) and Windows 8 RT. Windows 8 RT has only the "metro" UI and is under the hood a different operating system geared for tablets. Windows 8 Pro is the Windows 7 successor and is for regular computers and high end tablets. We only support Windows 8 Pro. Whether we ever have support for RT really depends on the demand.
The Windows installer is available on the Downloads page.