Proper Collision Detection

I need to wrap up a project for class and I've been struggling with collision detection. My world is based upon faeries and faeries must be able to fly up, down, left right. I've got the movement portion of it down, however, I have looked through all of the various resources available to me and I have yet to uncover a single tutorial that has helped at all.

Perhaps I'm overlooking something, but I need to stop the 'Hero' from underneath the ground or from flying too high above the world, in addition to avoiding collisions with buildings and any other terrain. The best help at this point would give me the basic structure of what the coding will look like and how I would compile all of it together to define my physics logic.

Thanks in advance for all of your time and consideration.

In addition, how might I go about having the hero being able to "cast magic"?

[djslater107]

A web site that you may find helpful is maintained by Dr Susan Rodger at Duke University: http://www.cs.duke.edu/csed/alice/aliceInSchools/