G'day Kenny

Try Debra Dalgleish's website, she has a mulitple Data validation listbox
for dependants which I think will help you with your task.

Somewhere to start, anyways!

http://www.contextures.com/xlDataVal13.html

It lets you select both directions, by that I mean, if you select a name
from listbox.1, it will filter everything that matchs into listbox.2 and
viceversa and so on.

Check it out, have a play.

HTH
Mark.