You'll need at least the following setup to play the game:
CPU: You'll need at the very least a dual core running at 2.5Ghz for the game to run properly.
RAM: 4GB of RAM should be more than enough
OS: Windows 7 with the latest service pack installed
Graphics: DirectX 10 compatible GPU with 512MB VRAM minimal
Storage: 500MB available space
Large and gigantic maps will require a better CPU, preferably a quad-core running at over 3Ghz