Excel 2007 : Dependent Dropdown (Data Validation)

Hey everyone, I have a somewhat different question about dependant drop down lists in excel 2007.

i have been actively searching dependant drop-down menus for excel for 2 days now, and i have not found an example that explains quite what im looking for.

the problem is that many of these tutorials explain Cascading dependant drop down menus, i.e. 3rd menu dependant on 2nd, 2nd dependant on 1st, almost as if they were in series.

I need a way to develop a dependant drop down menu that works in parallel, for example, I want to generate a drop down list that is dependant on 3 separate categories simultaneously. each of the 3 categories would be independant of one another and have their own drop down selection. The 4th drop down menu would be specific to each possible combination of the 3 independant categories.

In case that explination was too general, ill be more specific. I want to generate a list of available wire types based on 3 categories each having their own drop down menu. this is as far as i have gotten:

1.Run Type (Drop Down):
----->1. In Conduit
----->2. In Cable Tray

2.Wire Material (Drop Down):
----->1. Copper
----->2. Aluminum

3.Temperature rating (Drop Down):
----->1. 60°C (140°F)
----->2. 70°C (167°F)
----->3. 90°C (194°F)

The user will select from each of these 3 drop down menus, and will then be able to select from a fourth drop down menu displaying a list of the available wire types according to the specific combination of the 3 categories available. In total, there are 12 specific lists of available wire types based on every possible combination of category 1,2, and 3.

sorry if this explination is redundant but i wanted to be as specific as possible. I would attatch my file, but it is quite incomplete, and very messy. all i have is the first 3 drop downs, which were relatively easy to learn how to make. thanks in advance for any help.
much appreciated
matt