I'm not sure how fancy a solution you were looking for, but here is a simple way to get a reminder in Excel.
Put the date you need the reminder into a (hidden) cell. Name the cell "ticklerdate".
Somewhere front and center of your spreadsheet, put a big (maybe merged) cell with white font so it doesn't show, "Remember my wife's birthday!!"
Then set up conditional formatting such that when today()>=ticklerdate, the format of the cell goes to black print on neon yellow background and font size goes to 24+. That'll get your attention.
