It's About The Lottery. Oregon Lotto To Be Exact....?

Okay so with winning the powerball if I won the 74 million dollars how much would i actually walk away with. I heard that it is half that if you take it in a lump sum but that it's also 25% for federal and 8% for state as far as taxes go? How do I determine how much I get? Same goes with the Megabucks. THANKS!!!!!