Minimum requirements:

Windows:

OS: Windows XP
CPU: Anything better than 1.4GHz
GPU: Any GPU with 256mb VRAM or better
RAM: 1GB
HDD: 1.7GB

MacOS:

OS: Mac OS X 10.8 Mountain Lion
CPU: Intel Core 2 Duo 2.0GHz
GPU: Any GPU with 256mb VRAM or better OR Supports OpenGL 2.0
RAM: 2GB
HDD: 1.7GB

Linux:

OS: Ubuntu 12.04
CPU: Anything better than 1.4GHz
GPU: Any GPU with 256mb VRAM or better OR Supports OpenGL 2.0
RAM: 1GB
HDD: 1.7GB