How do I create nested dropdown lists?

How do I create nested dropdown lists?

I am customizing our CRM to support out company and we have leads that will come in from various industries, and sub groups of that industry, and sub groups of the subgroup.   For instance, Industry is Education, but then I need/want to know what grades the school has, and then if that school is private, public or charter.  So, how do I get the Layout to offer the user the ability to pic Industry1 in first picklist, and that choice triggers a 2nd picklist (industry2) and the choice they make in 2nd picklist begets a 3rd picklist (industry3)?  and so on, depending on the industry the lead is for?
I have done a google and bing search, and checked the forums, but only saw one post and the answer was to try it yoruself or ask in the forums.  Help??