Excel 2007 : Help with auto fill from drop down selection

Hi guys, need some assistance

If i set up a calendar drop down list in A1, how can i get A2 to Auto fill with the number of days in that month? Dependent on the Month selected in A1. If anyone knows can they please let me know before the big vain in my head pops

Thanks all

John

Look here for Dependent data validation: http://www.contextures.com/xlDataVal02.html

Create three categories (31 day months, 30 day monts, February) and 3 lists (1-31, 1-30 and 1-28/29)

it's not a manual drop down i need for the number of days, i need it set up so say for example i select JANUARY from a drop down list in A1, then A2 will display 31 automatically, If i select FEBRUARY in A1 then A2 will display 28 Automatically????