Andy is right there's no native version of Keynote on Windows but Keynote does allow for exporting .ppt files of your Keynote presentation - with some unwritten caveats. Unwritten in that Apple's magic-marketing-speak makes it sound like you can export with ease but it can be excellent at times and rocky in others. Simple presentations without any Keynote-specific transitions or builds do tend to convert into PPT just fine. You can also export a flat .PDF of your slides from Keynote which can be read on a PC. For the best results I export a QuickTime movie of my slideshow from Keynote which renders very faithfully including the transitions and builds on a Windows machine with QuickTime installed.