These are two interesting paragraphs from the link above: Also see above where maq brought clipping from a casting sheet that is interesting!
* Shelob WILL NOT BE in The Two Towers. Apparently, they've expanded the Frodo-Sam-Gollum-Faramir stuff quite a bit, and as such Shelob has been kicked to the beginning of ROTK. No word on how they'll end TTT. PJ wanted us to know so that "we wouldn't be disappointed." More Arwen too, they said.
* Fran Walsh wrote AND directed Gollum's backstory. So flashbacks of Smeagol and his birthday present will be in TTT.
Yep, she rides to Helm's Deep to deliver Aragorns reforged sword. Narsil is reforged in Rivendell at the beginning of the movie I hear.
Here's Arwen riding into Helm's Deep: