Nested "Data-> Valuation" within a conditional Statement

I could use some help.

I have four (4) columns of data formatted in "Drop Down" selections. I need to create an IF statement that captures the initial response and then provides a reduced choice of variables in the next successive drop-down list of variables. In essence, a drill down.

I'm at a loss, any suggestions would be greatly appreciated.

See if this link is of any help to you:

http://www.contextures.com/xlDataVal02.html

Jason