Data Validation And IF Statements

I�m a fairly basic excel user, I think I have a fair idea of what I�m trying to achieve.
I�ve tried to take the time to explain my query so if anyone is happy to help, I�ll definitely take the time to give a decent response.

I�ve broken it down abit.

Background

I�ve created a form for which users select a series of drop down boxes, as each drop down box has a value selected, the options available for the proceeding drop downs are filtered and the options then become limited.

In order, the drop down boxes are;
1. Select a Utility � the data validation source list is �utility�GasElectricity2. Select a Distributor List of 3 Gas Distributors the data validation source list is �ElectDist�List of 5 Electricity Distributors the data validation source list is �GasDist�If user selects Gas as a Utility as per dropdown list #1, then the option shown in �GasDist� validation source list will appear.

If user selects Electricity as a Utility as per dropdown list #1, then the option shown in �ElectDist� Validation source list will appear.

3. Select a Service the data validation source would be either �Eservice� or �GService�Special Read Investigation4. Select a Sub Type the data validation source lists are either �EReadSub, GReadSub, EInvestSub, GInvestSub�