Growing up in Ireland, we were always taught that Halloween was celtic/Irish, coming from the samhain festival, about the barrier with the spirit world and ours becoming thinner or some such. It was pretty much celebrated in the same way as the stereotype, less 'candy' more nuts and apples, also for some reason there would be a brack (read: tea cake) with a ring inside it. Always find it kind of annoying when people refer to Halloween as American, but what can you expect with American TV/Films everywhere.
http://en.wikipedia.org/wiki/Halloween#History
Its not traditionally celebrated in most of Europe as far as I can tell, plenty of different festivals, although it is certainly spreading around. Last year I was given advance warning that some of the grandkids of people in the neighbourhood were going to come trick or treating, I had fun making the front door/myself appropriately spooky. Some of the kids live mostly in France and hadn't seen Halloween before, they loved it. Of course there are two different Halloweens; the kids and sweets variety, and the young adults and alcohol variety. I've also had a whale of a time hosting the latter.