Not to defend the person who stole your story, but I think the Internet has so badly blurred our concept of plagiarism that some people may not understand what it is anymore.

Look at the number of web sites that copy language directly from other sites without attributing the information to an author. I was recently doing research on "kidney failure in dogs," and of the first five web sites I found, four of them said the same thing, in almost identical words. "Research" used to mean going to a number of sources and copying the pertinent information from each onto a note card, then summarizing it in your own words, with reference to the sources. Now it means going to Wikipedia (unless your teacher has warned you that they will be checking the Wikipedia entry, so you find a different site), highlighting the text, hitting "copy," and pasting the language that you have found into your own document. Since the person doing the "research" hasn't actually typed any of the text, they have no motivation to go to the additional trouble of stating it in their own words.

I don't read ff.net, but does it make you pledge anywhere that the person posting the story must be the actual author? Or do some people think they can simply post a story that they like?

So I realize that you're outraged, Kathy (and I would be too), but in a sense it IS a compliment to your writing. I'm going to have to look for your story and read it myself now.