Minimum:

OS: Windows Vista SP2 or Windows 7. Windows XP is not supported
Processor: Intel Core2 Duo E8200 2.66 GHz or AMD Phenom X3 8750 2.4 GHz
Memory: 2 GB for 32-bit OS or 4 GB for 64-bit OS
Graphics: Nvidia GeForce 8800GT 512 MB or ATI Radeon HD 3870 512 MB
DirectX: Version 9.0c
Hard Drive: 16 GB
Sound: DirectX 11.0c compatible
Additional: Broadband connection required for activation and multiplayer gameplay
Note: Windows XP Operating System is not supported
Further information: Available here

Call of Duty: Black Ops II screenshots