Prise off the dust cap after removing the wheel - underneath you'll find a large hexagon nut staked in place. Ignore the stake, undo the nut (conventional thread, turn anticlockwise) and the drum should pull off. If it doesn't, lightly tap with a hammer as you pull and rotate it...if its really stubborn you'll need a puller that bolts to the drum using the wheel bolts.
John
March 2008