Recommended setup is;
* Intel Core 2 Duo E6400 or AMD Athlon 64 X2 4400+ / 2.3 GHz processor
* 2048MB RAM
* NVIDIA GeForce 8800 GTS 640MB
* 12GB disk space
Windows XP, using DX9 is limited to "high" graphical settings, while Windows Vista, using DX10, can be set to "very high". According to Crytek the recommended system will run the game in high resolution at high/very high settings.