Upgrading Windows XP to Windows 8 on my Mac

I currently run Windows XP on my Mac. I recently upgraded to Mountain Lion, only to discver that Windows XP doesn't work with Mountain Lion. My question: Am I able to upgrade to Windows 8? Or will it not recognize that I already have Windows XP to even be able to upgrade from? The reason I ask is I cannot even access Windows at all. So my fear is, if I buy an upgrade, is there anything to upgrade since the Mac isn't even recognizing it anymore? Or do I need to buy the full Windows 8 and just install from scratch? Thanks for any advice because I am clueless.