I'm thinking about buying an IMac, and due to my military friends and other reasons, I might want a copy of Windows XP or Windows 7 on it with Parallels Desktop 6 for Macto go between the Windows Operating System and the Snow Leopard or OS X Lion . I realize that the Apple/Mac Operating System has very few security problems, and that I'd be inviting all those security problems into my MAC by running windows in it. QUESTION: Is Windows 7 Ultimate worth the extra cost to buy a full version copy, over Windows XP SP3 full version?...