Natural mod seems popular but if someone could explain how you install it onto a steam copy I'd give you my opinion.
comes an an .exe. just run in and choose the steamapps/crysis folder
tried that. didnt work for me. did it work ok for you?
Have a look at this thread started by TheCenturion :
http://forums.overclockers.co.uk/showthread.php?t=18235428
been following this.
Eagerly awaiting!
I'll do my best for you guys though