I've seen some reports from people who've called theaters and been told by employees that they hadn't heard anything about the preview nor had they heard anything about getting a replacement reel with the preview on it. Just seemed like it might be a good idea to call first and make sure it'll actually be there.
This whole business isn't sounding very organized...maybe the theater chains aren't handling it very thoroughly.
On the plus side, I see that at least 2 theaters in my area that didn't show LOTR in the first release are opening with it on Friday. And a theater that hasn't had it for a while is re-releasing it on Friday. Yay!!!