I want to have both versions. I was just looking on the offical LOTR movie site. The extended Two Towers DVD's are going to be different. The deluxe one that comes with the Gollum figurine is going to have an extra DVD with how the brought Gollum to life, ect..
On a side note, my parents finally got to see Fellowship (well, the first disk of the extended version, anyway; 2nd disk tonight). My dad's hearing isn't the best, so we turned on the subtitles. It's amazing how much dialogue I've never picked up on! Very interesting, and I'd recommend watching it that way once for anyone who thinks they know every word.