[Linnahiril Tinnufinwen]

In response to Boromir's question of why Theoden would move his people closer to Isengard, I believe that Theoden, at least in the movie, was unaware that the enemy knew he was going to Helm's Deep, or that they even knew it exsisted. I know that it is perhaps silly on Theoden's part to think that the enemy was so oblivious, but this is the impression that I got from the movie. Theoden takes his people from Edoras and transports them to Helm's Deep because he was under the impression that Sauruman would attack Edoras, and not know anything about Helm's Deep at all. The Orc armies would arrive at Edoras, and the Rohirrim would be gone, and Sauruman would not know where they had gone to.