I'd also like to know if these DVDs are subtitled. The older Avatar DVD collections did not have subtitles, only close captions, but unfortunately my portable DVD player doesn't display close captions, only subtitles.
@Felipe - they did release the series in other regional sets so if you can find a "Region 4 (Latin America) or Region 2 (Europe [Spain])" they may have dubbing, but most likely they will be subtitled in my opinion.
Since the discs in the Collector's Edition are the same as those in the original Book I box, they don't have anything extra on them, including subtitles. All the new extras are on the 7th disc and the new booklet.
kiansmom, many DVD players have a way to select closed captions on and off in a more buried menu, but I am not sure if your portable one will. All devices with screens over 13" are required by law to be capable of displaying cc's for the hearing impaired, but devices with screens smaller than 13" are exempt (I guess they assume if you need closed captions you won't be able to see a screen that small), so in those cases it is up to the manufacturer. I'd recommend playing around in the player's settings menus.