Some of these questions have already been answered quite adequetely, so I'll just skip them. Still, I do have some answers of my own.
1. Have you guys all read the book it is based upon, Mrs. Frisby and the Rats of NIMH?
I don't know where I'd be if I hadn't :) (I also read the first half of
Racso. I wasn't able to finish it, though - perhaps in the future).
2. Which do you like better, the book or the movie?
Personally, I tend to meld the two together in my mind, using the book as a base and filling the gaps with details from the book, similar to what Simon has said. That way, I get to have a deluxe package of SoN's fantastic visuals and inspiring presentation and the book's character development and plot progression (though there was plenty of that in the movie as well).
3. Why do you think the story in the movie was so dramatically altered from the original story in the book?
People have said this already, but I thought I'd restate it in my own words. The alterations have much to do with the conventions of the medium (much like Shakespeare had to adapt his plays to suit the conventions of Elizabethan drama). Books are generally very detail-oriented; they tell the story using images made from description and exposition with written language. Movies, on the other hand, are by nature visual productions, relying on movement and action to advance the story. Changes, therefore, had to be made to the original storyline in order to make it conform to the movie medium. Conversations were slimmed down, more action was added such as the tractor and duel scenes, and characters were presented more explicitly, with more emphasis on their various quirks (some only marginlly related to the originals).
The movie isn't just an more colourful, fast-paced version of the book, but is also a means of interpreting the book's themes. The greater emphasis placed on Mrs. Brisby's (Mrs. Frisby in the book) story serves to likewise place an emphasis on the theme surrounding her story, that is, the motherly love is has for her family and the strength and courage that she, as a good mother, must possess in order to succeed. This was actually only a secondary element in the original story, where greater emphasis was placed on the rat's story and its theme. Still, this shift in focus probably reflects the intention of Bluth and his team; they probably found something particularly inspring (as I'm sure many of you have) about Mrs. Frisby's sense of maternal duty and her strong sentiment of sacrificial love. The rats and their story still plays a major part, of course, but their view of things is more or less used to complement and supplement the primary theme that arises from Mrs. Brisby's experiences.
There are also dramatics to consider, the "spicing up," if you will, of the plot and characters in order to better utilize the tools of the medium. Characters such as Jeremy and Justin are given a makeover in this regard; their personalities are exaggerated and changed, yet in such a way as to complement their characters and to contribute to the overall feeling of the film. The use of Jenner as the scheming antagonist also brought about this general effect, as was the protrayal of Dragon as a demonic, savage entity, much more violent and hideous than in the book. There was also the portrayal of Nicodemus as a powerful 'wizard' to add an element of mystery and fantasy to the story (the Stone functions the same way). The rats in general (plus some other characters like the Brisby children) are given a more anthropomorphic feel and design in order to appeal to our visual senses, aesthetic or otherwise.
4. Do you think the movie would have been better if it had remained more faithful to the book?
Not necessarily. As I have mentioned before, too close an adaptation to the book would have left the story somewhat dry. However, that said, there are certain elements from the book which they could have used to flesh out the plot. They could have given Timothy more screen time (and some more lines, for that matter) in order to evince his sense of quiet courage even in the face of death. They could have given us some more details concerning the rats and their daily life in the colony (perhaps even showing us some rat children). Also, they could have fleshed out Nicodemus' story with a bit more detail, especially concerning their stay at NIMH. Another aspect which I felt could have been included (and which I missed from the book) was the character of Isabella. Despite her minor role in the original story, I felt that having just a brief scene with her would have served to supplement our view of the rats and provided us with a definite female presence in the colony (the only other women in the colony appear as council members in the background). Plus, it would have also supplemented Justin's character, if you know what I mean ;)
5. Why exactly is Nicodemus a wizard with magical powers in the movie, how did he become that way, and where did the stone come from? How does all that fit in with the plot about street rats genetically altered to be superintelligent?
Aside from what I've already said concerning adaptation, there are several different ways to approach this intriguing question. One speculation involves the nature of the NIMH treatments (recall Christopher Silva's
Children of NIMH story, which deals with this side of the question); we know that it made them smarter and physically stronger/bigger, but was that all it did? Did the formula have other effects as well? In this case, the hidden abilties given to them by NIMH was made manifest in the Stone, which seems to have been fashioned by Nicodemus, if he did do such a thing.
Another hypothesis would involve Jonathan's hidden heritage (someone else mentioned this on NIMHMuck...you know who you are ;)). Nicodemus mentions that Jonathan meant to give it to Mrs. Brisby, implying that he is the primary owner and that Nicodemus was only its keeper (I could be wrong, of course). If this is the case, then what other secrets does Jonathan have? How much of a 'normal' mouse was he before he was taken to NIMH? Are there others like him? Questions...
Still another supposition rests on the "found-it-on-the-way" assumption. The rats (and the two mice) may have just stumbled across the Stone during their journey and found amongst themselves some who would put it to the best use (Nicodemus and Jonathan). This may seem rather prosaic, but think about this; where did the Stone come from, then? Is it some rare mineral/element that can be found in the Earth, or is it something manufactured? What is the source of the Stone's abilities? What if it didn't come from Earth but...someplace else? (Recall HMS Eagle's
The Stone Master, except maybe without the aliens :) It also deals with another question; if Mrs. Brisby and the other 'normal' animals are, well, normal, then since when could they communicate like that? Plus, Mrs. Brisby seems to have been married to Jonathan for a while now...longer than she ought to...)
From a more technical standpoint, the portrayal of Nicodemus as a 'wizard' probably comes from the presentation of the film as a fantasy tale, reaped in swords, sorcery (though that latter element is dealt with very subtlely), and wonder. Still, because of the science fiction element, one cannot really call it 'sorcery' as we usually define the term. As I mentioned before, the NIMH treatment may have given the rats the ability to detect something above the level of normal animals and humans, something that permeates the atmosphere of the world, waiting to be discovered and utilized, whether for good or ill...
The first person to talk about the "Force" gets bopped in the head :P
What do you know? It looks like I answered most of the questions after all :) Well, enjoy my ramblings, and till next time...