So I recently got a new HDD, did a clean install of OSX, and while I was at it, I bought Windows 7 Ultimate 64 bit. Previous to the HDD upgrade, I was running Windows XP. The only thing I use Windows for is Games (Bad Company 2) and Quickbooks. That's it. I thought Windows 7 would help run games smoother, but it turns out it's more choppy now and the framerate has dropped. TL;DR: Can I install windows XP over windows 7 without a problem? Or do I need to do something else? Would I have to do a clean install of the whole OS's? Thanks in advance.