Minimum:

Supported OS: Windows XP or Windows Vista***
Processor: 2.8 GHz or faster (XP) or 3.2 GHz or faster* (Vista)
Memory: 1.0 GB RAM (XP) or 1.5 GB RAM (Vista)
Graphics: 256 MB**
DirectX Version: DirectX 9.0c (included)
Sound: DirectX 9.0c compatible
Hard Drive: 12GB
* Supported Processors: Intel Pentium 4 2.8 GHz (3.2 GHz for Vista) or faster, Intel Core 2.0 GHz (2.2 GHz for Vista) or faster, AMD Athlon 2800+ (3200+ for Vista) or faster.
** Supported chipsets: NVIDIA GeForce 6800 GT or greater; ATI Radeon 9800 Pro (Radeon X800 Pro for Vista) or greater. Laptop versions of these chipsets may work but are not supported. Integrated chipsets are not supported. Updates to your video and sound card drivers may be required.
*** Currently only the 32-bit version is available.

Crysis