BeforeEdit Event

Hi Folks,
I have some working code in the BeforEdit event.

Now I ha a field called BIRTHDAY in the db which is also on the Edit page.

This a one textbox where people may enter their date of birth.
How can I add 3 dropdown values that hold pre-entered day, month and year, while when saving it only writes to the db field in format dd-mm-yyyy

Also when users want to edit this field, the edit page must read out the dd-mm-yyyy so the right values are displayed in the comboboxes.
TIA
Hans