Treyarch has finally released the minimum PC system requirements for BO2. Although the requirements aren't that much more demanding when compared to the original Black Ops, support for Windows XP has been dropped.
The BO2 game engine has been upgraded to support DirectX 11, which automatically means that there is no support for Windows XP - this doesn't come as a surprise since PC games nowadays, like Battlefield 3, don't support Windows XP. The game still uses the old Black Ops engine, but it has received number of improvements, including performance optimizations. The PC version features enhanced lighting, anti-aliasing, ambient occlusion, and other enhanced effects, unlike the Xbox 360 and PS3 versions.
Treyarch also revealed that the new game engine supports proprietary anti-cheat technology, so this most likely means that the game has built-in support for PunkBuster.