Spray them down with penetrating oil, like Liquid Wrench, give it some time to do its thing, then try again.
If that doesn't work, you could try warming the hub with a heat gun (aluminum expands & contracts at a different rate than steel, which could help break the bond) and/or a bigger hammer.
If it's not too late, you should thread an old nut onto the end of the axle you're pounding on to help prevent damaging the threads too badly and making it non-reusable.
Last edited by Torchy McFlux; 06-10-09 at 05:04 AM.