Everybody except the OP knows. Crysis is pretty well optimized. For full performance you will need a C2D or even a C2Q for better performance. But to run the game with minimum detail you will not need over a 2.8GHz at the max. PERIOD
The game will need a minimum of 512-768MB RAM(1GB for Vista). For good performance you will need 1.5-2GB RAM on both XP and Vista(preferably atleast 2GB for Vista). The game may run better on Vista.
The minimum GPU will be a 128MB Geforce 6200/6600, I agree, but not 256MB. Also, Radeon 9700Pro/9700 and 9800Pro/9800 would do as well. FX series may face problems.