I read that Narsil will not be shown until RotK, which will open with the reforging of it in Rivendell...
However, Helm's deep is described as including elves in the battle, so I'm sure you're right about Arwen showing up. Certainly we can't have the requisite "hollywood romantic scene" be missing from Part 2 of the trilogy. (I'm rolling my eyes here, lol)
I meant, Helm's Deep including the elves in the battle as part of the description of the scene from the movie (not the book).
I've seen pictures of Arwen at Helm's Deep. All the pictures of Aragorn at Helm's Deep shows him with the sword. So... who knows.
And you are right. Have to have the romance. (I'm rolling my eyes too)
Where have you been, I've missed you!