Validation lists that change based on a selection from another lis
 

As my subject line implies, I am trying to figure out how to change a
validation list based on a selection (or selections) from another validation
list. I found a resource that shows how to do it for 2 list, but I have 3
list and one of them is based on the selections from the other two.
So what I need help with is how to setup a validation list that changes
based on the selections from two other validation lists. Any help will be
greatly appreciated. This is a top priorty for us right now.
Thank you.