That Crysis certainly is a resource hog, ain't it? Bet you've seen asthmatic oxen pull more weight than your aging PC. Stupid D3D 10 not being all D3D 10. The nerve!
Consider, then, this tweaking tutorial from the folks over at TweakGuides, as an inhaler full of soothing meds. Spray it, suck it down, and let your PC breathe again.
Or we could skip the silly metaphors and you could just click the link below.
Crysis Tweak Guide [TweakGuides]