Radio buttons are a neat way to enable only one thing to be selected. The downside is that you need to add macros on the back end to make them work.
The tutorial below (recorded in Excel 2007, but 2003 options also explainded) offers you a way to use data validation to ensure that only one cell has data entered. It’s not quite as good as a radio button, because in order to change your selection you have to delete the original then insert the new, whereas radio buttons do that for you. But if that’s not a big overhead, then please consider this option over radio button macros.
The second part of the tutorial shows you how to set up conditional formatting so that the other selection turns grey once you’ve filled one in.
Leave a comment if you want to know how to do this for more than 2 cells, and I’ll record another tutorial to demonstrate.[youtube https://www.youtube.com/watch?v=dS_ZTx7H58I&hl=en&fs=1]
Demo spreadsheet: not_radio_buttons.xls