Peanut powder as such requires that most of the peanuts' natural oil be pressed out, this can be difficult without expensive equipment. You can very finely chop (dry roasted) peanuts into a rough grind similar to coffee. How much of a "powdered" end product depends largely on how much oil your starting peanuts have, more info can be found searching: whattocooktoday.com/how-to-make-peanut-powder