We used to celebrate both in England even long ago, with one difference - no trick or treat. Halloween was just for costume parties, telling ghost stories, and so on. I remember the debates whether to have a halloween party or a Guy Fawkes party. Of course, you could combine both, with costumes and fireworks. I think that's the best idea.

Well, two differences, really. We didn't have pumpkins. The Jack'o'lantern was a turnip, too small for a human skull really, but it looked much more like a death's head than a pumpkin does if you disregard the size. Much more difficult to carve, though. You wouldn't let a child carve it, as they might slip and cut themself.