Sorry for a long absence, one of the companies that I work for was taken over and that used up all my gas in the last month or so. So now I am back, here is a good article on Excel by Susan Harkins that sheds some light on the mysterious world of "Structured Excel programming".
Susan writes... Excel's basic validation is usually adequate, but sometimes you may need an on-the-fly solution. Here are the steps for using VBA to make it happen. Valid data is the cornerstone of any application. Thanks to Excel's Data Validation feature, input values can be tested and accepted or rejected based on criteria you specify. One of the easiest ways to validate data is to restrict users to a list. You can even update that list in one of two ways: You can manually add new items to the source list or you can allow users to enter new values using the data validation control itself. In this article, you'll learn how to update and alphabetize a data validation control's source list using VBA. Read more on Excel Combo boxes here