McKellan put a quick end to this rumor. Arwen does NOT accompany the Fellowship in the movie. He also responds to a question about Gandalf's sword Glamdring. I worked with Bill Hobbes years back when I played Hamlet onstage - dagger and rapier. I have never had any general fight training, so each time I have to wield a weapon I start from scratch.
Fighting is easier onscreen than onstage.
The camera rarely sees the full figure, whose silhouette is crucial to convince a theatre audience. Hence the use of doubles who save the actors' time and bloodied knuckles. You can be pretty sure that when you can't see the characters' faces during a film fight, that doubles are being used. Below are a pair of pictures that appeared at a licensing show. Originally appeared on Dark Horizons but TheOneRing.net managed to get larger versions.