It may seem odd at first but once you understand the pricipal real world glass object will take on a new meaning. Robin Wood wrote a really good article about glass and almost every other glass tutorial is based on her article.
http://www.robinwood.com/Catalog/Tec.../LWTutSet.html
Also this next site is a great resource for tutorials that are on the internet.
http://members.shaw.ca/lightwavetutorials/Main_Menu.htm
-Lee