Well, all the editions now are printed with his original writings that appeared in the British versions. I believe I only ever read British versions, except for an "American" LWW in my old school's library, in which I remember the Fenris Ulf thing. I prefer Maugrim, but I liked what he said about "written as deep as a spear is long in the trunk of the world ash-tree." Oooh. That gave me shivers. I like it better than the "fire stones on the secret hill" or whatnot. I live in the U.S., but it's hard to come across the "American" versions because they're from a long time ago and newer editions are not printed with those changes. The interesting thing is that American LWW I spoke of had LWW numbered as the first book in the series. I feel I was fortunate to have found it and read it first, but it was the most popular and well-known of the series so I'm not too surprised.
I would like to quote something I found on Google from another Narnia-related forum/thread, because it talks about some changes in VDT.
Paul F. Ford wrote:From the entry DREAMS in the forthcoming fifth edition of my Companion to Narnia (ALL CAPS indicate cross-references to other entries in the book):
It is in VDT, in the experience of the DARK ISLAND, that the subject of dreams becomes most vivid, and Lewis considered this so important that he made several substantial changes in the text between the British and old American editions of the book. After the DAWN TREADER emerges from the darkness, the British edition (now the English edition for the world) says: “And all at once everybody realized that there was nothing to be afraid of and never had been. They blinked their eyes and looked about them.” In the old American editions, Lewis deletes these two sentences entirely, thinking perhaps that he was making too little of the reality of which they were afraid. He replaces these sentences with one long, beautiful simile, one of the finest he ever wrote:
And just as there are moments when simply to lie in bed and see the daylight pouring through your window and to hear the cheerful voice of an early postman or milkman down below and to realize that it was only a dream: it wasn't real, is so heavenly that it was very nearly worth having the nightmare in order to have the joy of waking; so they all felt when they came out of the dark.
This is a major change: Lewis here is highlighting the JOY of waking after a night of FEAR.
The next change comes by way of an omission. Both editions print the expectation the crew has that the ship would be covered with grime and scum. The British edition goes on to say: “And then first one, and then another, began laughing. 'I reckon we've made pretty good fools of ourselves,' said Rynelf.” The old American editions delete both sentences, thereby removing another denigration of the seriousness of night fears.
When Caspian asks what boon Lord RHOOP wishes the KING to grant, the British edition prints:
'Never to bring me back there,' he said. He pointed astern. They all looked. But they saw only bright blue sea and bright blue sky. The Dark Island and the darkness had disappeared forever.
'Why!' cried Lord Rhoop. 'You have destroyed it!'
'I don't think it was us,' said Lucy.
Lewis reconstructs this entirely for the old American editions:
“Never to ask me, nor to let any other ask me, what I have seen during my years on the Dark Island.”
“And easy boon, my Lord,” answered Caspian, and added with a shudder, “Ask you: I should think not. I would give all my treasure not to hear it.”
This is perhaps the greatest difference between the editions. The British edition says that our Dark Islands in life can be destroyed; the old American editions are much more real in their assessments.
Finally the old American editions, having deleted the destruction of the Dark Island, add a parting note about the experience. Both editions print the sentence: “So all afternoon with great joy they sailed south-east with a fair wind.” To this the American editions add the independent clause: “and the hump of darkness grew smaller and smaller astern.”
Hmmm. I see what they're getting at. The old "American" versions made the Dark Island seem a very real, serious, frightening thing, whereas the British version sort of made light of the Dark Island. Of course, I don't think Lewis made those changes because he felt people in the U.S. would be more keen on them, but really just because he saw it as an opportunity to edit some things he wanted changed. People don't see it that way now, but I sort of feel like they should. I don't think it's a case of "Oh, American audiences will like this better", which would be a reason to keep it to the original British versions, but that Lewis actually wanted to make some changes. Of course, there are some things I like about his original text and some things I like about his changes. They both exist, so I guess we can pick and choose.
I've never had access to them and I don't think they ever were available in Australia. I think that the cartoon version of LWW referred to Fenris Ulf and maybe some of the other productions. This startled me as the character I knew was Maugrim. And now I know what a main difference there might have been in VDT. 
