Very low fps on crysis warhead?

i have a gtx 460 700mb or something not 1gb, 2gb drr2 ram, phenom x4 2.4ghz but when i play crysis on just high i get 18 fps when i should be getting at least 24 to 30 fps, i am running beta driver on card because main driver gave me crap fps on everything, any one got an idea.