Generating 'pop-up' calendar upon clicking a cell

Hi Francis. The simple answer to this question is: you need an add-in! Otherwise you're looking at a VBA coding job - there is no standard function in Excel to achieve this. Here are two links which go into further detail:

http://www.fontstuff.com/vba/vbatut07.htm
http://www.office-kit.com/excel_calendar/

Hope this helps,

Anthony