They're usually seized between the hub and the center of the drum and it almost always takes a few heavy solid hits as close to the center as you can without hitting the studs to get it to free up. Put some old nuts on the studs and hit the drum hard!! Last resort heat it up fast and hot with an oxyacetylene torch near the center of the hub as CFD244 suggested. If you haven't got this done yet PM me and I can bring my torch over to your place...
