Need calendar hack to use an additional displayed date

[jilly]

The public calendar now automatically shows up people's birthdays at the top, with the litte heading:
Today's Birthdays: and then lists any members' name whose birthday it is.

I would like to add another field to the calendar, for people to input an 'Anniversary Date', and then would like that date to show up automatically, just under the birthdays. - so it would say:
Today's Anniversaries: and then list any member's name that entered an anniversary into the public calendar.

How can I accomplish this?
Thanks in Advance
j