I have a brand new MacBook, my first new Mac since my old Bondi Blue iMac. I've never run Parallels before, and can select any version of Windows (I have an MSDN subscription.) Which is the preferred Windows OS for this purpose? XP, Vista, Windows 7? 32-bit or 64-bit? I simply want to use it to occasionally run some Windows-specific software. Nothing too intense, mostly Office 2007 and a few other custom apps.