Breaking it shouldn't be a problem... heck, I've a friend who's joked quite a bit about taking one of her various Implements of Destruction to a UC Narsil to do that very thing.
While I don't know about the one you have, wallhangers like that tend to made from a stainless steel that is heat treated to be relatively hard, and hence brittle. It will most likely be a devil to cut, but easy to break.
The trick is, you're not likely to get the same break pattern as in the movie, but rather a simple snap in two.
SO.. what I'd do in your place is dissassemble the sword, and go over the area you want to cut with a propane torch (or heck, stick it in a forge if you have one.. though I'm assuming not). Do this in low light, you want to be able to see the metal changing color.
When it gets an even dull red, you can stop heating it. This will take some time with a torch, but will eventually happen. Of course, have some good way of holding or securing the blade so the heat doesn't burn you (or carry up the blade and burn something else). You may want to do just one small area at a time.
Next.. just leave it to air-cool. It'll take a while.
Since the metal has cooled slowly, it will now be relatively soft and MUCH easier to cut. (It will also ding easier, so if for some reason you want the edges hard again, you'll have to re-heat it and then cool it quickly by dunking it in water or oil to cool).
This will discolor the blade, so you'll likely need to repolish it after this. That, or enjoy the pretty purple-rainbow-gray colors and say it was the heat of Sauron's embodiment that helped destroy Narsil.
Hope this helps.
