Mafia II System Requirements

Minimum System Requirements

Operating System: Windows Vista with Service Pack 1 / XP with Service Pack 3
Processor: Intel Core 2 Duo running at 2.8 GHz or AMD equivalent
Memory: 2 GB of RAM
Hard Drive: 20 GB or more
Video Card: 512 MB (GeForce 9400 or ATI HD3450)
Sound Card: DirectX 9.0c compatible
Optical Drive: DVD-ROM running at 1X
DirectX: DirectX 9.0c
Input: Keyboard & Mouse

Recommended System Requirements

Operating System: Windows Vista with Service pack 1 / XP with service Pack 3
Processor: Intel Core 2 Quad running at 2.5 GHz or AMD equivalent
Memory: 3 GB of RAM
Hard Drive: 20 GB or more
Video Card: 1 GB (GeForce 9600 or ATI HD3870)
Sound Card: DirectX 9.0c compatible
Optical Drive: DVD-ROM running at 8X
DirectX: DirectX 9.0c
Input: Keyboard & Mouse

The requirements are not 100% sure. Source here.