On what topic are the animals divided in Orwell's Animal Farm? What's Snowballs platform? What is Napoleon's platform?

The whole farm was deeply divided on the subject of the windmill. 

The farm is divided on the issue of Snowball’s windmill.  Snowball believes that modernizing and electrifying the farm will be good for all of the animals.  He works out extensive plans.  Some of the animals are concerned, however, that the windmill will be too much work. 

Snowball did not deny that to build it would be a difficult business. … But he maintained that it could all be done in a year. And thereafter, he declared, so much labour would be saved that the animals would only need to work three days a week. (Ch. 5) 

The greatest opponent of the windmill is Napoleon.  He opposes all of Snowball’s ideas.  Snowball has all of the animals placed into committees and is trying to organize them.  He tries to teach all of the animals to read.  Napoleon thinks that all of this is a waste of time, but his greatest objection is the windmill. 

Napoleon, on the other hand, argued that the great need of the moment was to increase food production, and that if they wasted time on the windmill they would all starve to death. (Ch. 5) 

Snowball and Napoleon both try to convince the animals that they are right.

The animals formed themselves into two factions under the slogan, "Vote for Snowball and the three−day week" and "Vote for Napoleon and the full manger." (Ch. 5) 

Napoleon runs Snowball off the farm, saying that he is a traitor who was working with the humans.  Then, miraculously, it comes out that the windmill was his idea all along and he is going to do it.  Napoleon needs the windmill, now that Snowball is gone, to keep the animals busy.  His goal is to make sure it never gets finished so the animals are always building it and he can work them constantly.

The windmill, representing technology or innovation, is an example of how the animals idealized Animal Farm.  Napoleon used this idealism against them, making sure to take over all aspects of life.  All Napoleon cares about is power, but Snowball really did have the interest of the animals in mind.