I don't have a D90, but the manual says that all you have to do is highlight the control that you want to use in the Select Picture Control menu - the first item in the Shooting Menu, and press OK. It sounds simple enough, where exactly are you having problems?
Thanks Chris...I finally did get it to work late last night. I have no idea what I was doing wrong, but the icon never would appear on the LCD when I hit "info" to see if it had accepted the change.
Works now...so it was obviously operator error.