Here's how to do it: Roll along at a slow to moderate speed with your feet in the forward position. Begin by snapping down on your tail, and dragging your front foot upwards. As your front foot is moving towards the nose, slide it off the edge (as you would for a kickflip). This is were the forward stance becomes crucial, you need to spread your legs to allow the board to flip through them, but without rotating your body as you would for a frontside 180 kickflip. Wait until the board is level, catch it, and land on the trucks, preferably catching it with your front foot. If you performed the hardflip correctly, the board should have done half a backflip and a twist.
It's important to watch people perform this trick in order to get a better understanding.