Using Lists in Excel 2003

[Kathi]

I have a spreadsheet with 12 months and under each month are 6 columns of
information.

I am trying to come up with a way that on a blank worksheet, you can enter a
number or letter (i.e 1 for January, 2 for February, etc or Jan for January,
Feb for February, etc) I was told there may be a way to do this using "lists"
but I am not familiar with them. Any ideas?

Thanks.