windows 7 isn't even new, most of its a blantant rip from features that already existed in Ubuntu or Linux. As long as you're running 64bit XP which pro is, then you should be fine as long as its compatible with xp. (and since they haven't updated the engine since CoD4, it most likely will)
Yes, you can play it.But best is the Windows 7 64bit.Windows 7 64bit is the most compatible operating system to almost all games. Crysis 2 which has the best graphics in the world requires Windows 7 64bit, and Windows XP is the minimum requirement.