In an attempt to answer Charon's and others questions, here's what I've been able to gather on the Arwen, and Eowyn question.
WARNING: SPOILERS AHEAD SO DON'T READ THE FOLLOWING IF YOU DON'T WANT TO READ A COUPLE OF DETAILS ABOUT THE MOVIE.
Arwen takes the place of her brother, Glorfindel as previously stated during the Flight to the Ford. I have to say that I was really taken aback by this and thought that this was a negative change especially in the light of Liv Tyler playing the role.
Several things have actually changed my mind on this.
#1 Peter Jackson really thought that it was going to be really difficult for audiences to buy the deeper love story behind Aragorn and Arwen on screen based just a very fleeting glimpse of Arwen in "1st" book. This is especially important in the light that one of the main reasons Aragorn wants to re-establish his rightful throne is based on his love for Arwen. With that in mind they thought it was necessary to give Arwen a little bit of time so that audiences will develop an emotional attachment with Arwen as well as an emotional connection with Aragorn's motivation as well since this love story has a central part to play. This makes a lot sense to me. I think it actually works out well as well that Arwen in the movie really just takes the place of Glorfindel, her brother anyway. It is conceivable that she could have easily been the rider that carries Frodo across the Ford vs. Glorfindel.
#2 From accounts I've read by Tolkien enthusiasts worried about the same thing, Liv Tyler actually plays the role of Arwen quite well. Of course I haven't seen the performance but I have to say that seeing even the short line she has in the trailer she delivers convincingly and I have to say even for a brief second I was seeing Arwen alive on screen and not Liv Tyler. The jury is still out for me I guess but at this point I think my fears have been relieved.
BTW- Arwen isn't a part of the Fellowship so don't worry about that. And Eowyn is still in the story- played by Miranda Otto.
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