I have this new pc(Q6600 @ 2.88Ghz stable atm, 8800GTX, 4 gig of ram), and everything can be set to very high, except for Terrain details, it can only be set to Normal or lower. I've heard of people having this kind of problem too, and they seem to have solved it by editing their armaconfigs, what i wanna know is the name of the variable that should be in the config.
Oh and i'm running vista 64-bit.