Entourage validating and copying link data

I have an Excel 2010 workbook that contains a number(18) of worksheets.

I have one sheet named "Data" that contains a number of named ranges that I use in data validation lists on the main worksheet for the new book.

You can also show an Error Alert that appears only after users enter invalid data.

You can choose from three types of error alerts: Warn users that the data they entered is invalid, without preventing them from entering it.

Hello - I have been trying to come up with a data list validation that only accepts either Y or N from a dropdown menu.