You are free to copy, and manipulate the example code in this tutorial as long as it is for non-commercial use. For most people that means: "do whatever you want with it". I would prefer that if you use anything from this tutorial, that you include a small comment in your HTML code telling that you learned how to make layers from this web site - http://www.golden.net/~steinman/html/layers/
An good example would be:
<!-- To learn how to make layers go to http://www.golden.net/~steinman/html/layers/ //-->
The use of any information from this website for commercial purposes without my consent will be subject to all applicable laws.