Using macros or code to unhide columns.

I have a spreadsheet that features drop down menus and multiple columns in order to log services provided by a grant-funded program. The intention is the publish this document and distribute to staff. In order to streamline the document, the desire is to hide all columns until required for data entry. For example, when logging a new service, you will begin to select options from drop-down menus. By selecting our "WIA" grant for example, in one cell, I wish to automatically unhide the column where those grant-specific service categories are listed. Then, upon selecting the category from the newly-revealed column of drop-down menus, I wish to automatically unhide the specific services. I have a bank of reference values for my drop-down menus hidden off to the side. For example: By selecting "WIA" in column P, I want column R unhidden. By selecting "CAREER GUIDE" in column R, I want column T unhidden, etc. There are more situations, so a general code in which I can insert my own column and value selections would be appreciated. Thanks.

I am using Excel 2010 on Windows 7 Professional.